diff --git a/Facepunch.Steamworks/SteamNative/SteamNative.SteamApps.cs b/Facepunch.Steamworks/SteamNative/SteamNative.SteamApps.cs
index 61114d5..2f28d3c 100644
--- a/Facepunch.Steamworks/SteamNative/SteamNative.SteamApps.cs
+++ b/Facepunch.Steamworks/SteamNative/SteamNative.SteamApps.cs
@@ -184,6 +184,7 @@ public CallbackHandle GetFileDetails( string pszFileName /*const char **/, Actio
 			callback = platform.ISteamApps_GetFileDetails( pszFileName );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return FileDetailsResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
diff --git a/Facepunch.Steamworks/SteamNative/SteamNative.SteamFriends.cs b/Facepunch.Steamworks/SteamNative/SteamNative.SteamFriends.cs
index 822fb33..6734548 100644
--- a/Facepunch.Steamworks/SteamNative/SteamNative.SteamFriends.cs
+++ b/Facepunch.Steamworks/SteamNative/SteamNative.SteamFriends.cs
@@ -98,6 +98,7 @@ public CallbackHandle EnumerateFollowingList( uint unStartIndex /*uint32*/, Acti
 			callback = platform.ISteamFriends_EnumerateFollowingList( unStartIndex );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return FriendsEnumerateFollowingList_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -193,6 +194,7 @@ public CallbackHandle GetFollowerCount( CSteamID steamID /*class CSteamID*/, Act
 			callback = platform.ISteamFriends_GetFollowerCount( steamID.Value );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return FriendsGetFollowerCount_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -429,6 +431,7 @@ public CallbackHandle IsFollowing( CSteamID steamID /*class CSteamID*/, Action<F
 			callback = platform.ISteamFriends_IsFollowing( steamID.Value );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return FriendsIsFollowing_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -446,6 +449,7 @@ public CallbackHandle JoinClanChatRoom( CSteamID steamIDClan /*class CSteamID*/,
 			callback = platform.ISteamFriends_JoinClanChatRoom( steamIDClan.Value );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return JoinClanChatRoomCompletionResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -475,6 +479,7 @@ public CallbackHandle RequestClanOfficerList( CSteamID steamIDClan /*class CStea
 			callback = platform.ISteamFriends_RequestClanOfficerList( steamIDClan.Value );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return ClanOfficerListResponse_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -516,6 +521,7 @@ public CallbackHandle SetPersonaName( string pchPersonaName /*const char **/, Ac
 			callback = platform.ISteamFriends_SetPersonaName( pchPersonaName );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return SetPersonaNameResponse_t.CallResult( steamworks, callback, CallbackFunction );
 		}
diff --git a/Facepunch.Steamworks/SteamNative/SteamNative.SteamGameServer.cs b/Facepunch.Steamworks/SteamNative/SteamNative.SteamGameServer.cs
index 507141f..bc8d46a 100644
--- a/Facepunch.Steamworks/SteamNative/SteamNative.SteamGameServer.cs
+++ b/Facepunch.Steamworks/SteamNative/SteamNative.SteamGameServer.cs
@@ -50,6 +50,7 @@ public CallbackHandle AssociateWithClan( CSteamID steamIDClan /*class CSteamID*/
 			callback = platform.ISteamGameServer_AssociateWithClan( steamIDClan.Value );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return AssociateWithClanResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -97,6 +98,7 @@ public CallbackHandle ComputeNewPlayerCompatibility( CSteamID steamIDNewPlayer /
 			callback = platform.ISteamGameServer_ComputeNewPlayerCompatibility( steamIDNewPlayer.Value );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return ComputeNewPlayerCompatibilityResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -156,6 +158,7 @@ public CallbackHandle GetServerReputation( Action<GSReputation_t, bool> Callback
 			callback = platform.ISteamGameServer_GetServerReputation();
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return GSReputation_t.CallResult( steamworks, callback, CallbackFunction );
 		}
diff --git a/Facepunch.Steamworks/SteamNative/SteamNative.SteamGameServerStats.cs b/Facepunch.Steamworks/SteamNative/SteamNative.SteamGameServerStats.cs
index 14cb187..706408c 100644
--- a/Facepunch.Steamworks/SteamNative/SteamNative.SteamGameServerStats.cs
+++ b/Facepunch.Steamworks/SteamNative/SteamNative.SteamGameServerStats.cs
@@ -74,6 +74,7 @@ public CallbackHandle RequestUserStats( CSteamID steamIDUser /*class CSteamID*/,
 			callback = platform.ISteamGameServerStats_RequestUserStats( steamIDUser.Value );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return GSStatsReceived_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -103,6 +104,7 @@ public CallbackHandle StoreUserStats( CSteamID steamIDUser /*class CSteamID*/, A
 			callback = platform.ISteamGameServerStats_StoreUserStats( steamIDUser.Value );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return GSStatsStored_t.CallResult( steamworks, callback, CallbackFunction );
 		}
diff --git a/Facepunch.Steamworks/SteamNative/SteamNative.SteamHTMLSurface.cs b/Facepunch.Steamworks/SteamNative/SteamNative.SteamHTMLSurface.cs
index 1d6b917..3f434bb 100644
--- a/Facepunch.Steamworks/SteamNative/SteamNative.SteamHTMLSurface.cs
+++ b/Facepunch.Steamworks/SteamNative/SteamNative.SteamHTMLSurface.cs
@@ -68,6 +68,7 @@ public CallbackHandle CreateBrowser( string pchUserAgent /*const char **/, strin
 			callback = platform.ISteamHTMLSurface_CreateBrowser( pchUserAgent, pchUserCSS );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return HTML_BrowserReady_t.CallResult( steamworks, callback, CallbackFunction );
 		}
diff --git a/Facepunch.Steamworks/SteamNative/SteamNative.SteamInventory.cs b/Facepunch.Steamworks/SteamNative/SteamNative.SteamInventory.cs
index 75da1b4..d6de777 100644
--- a/Facepunch.Steamworks/SteamNative/SteamNative.SteamInventory.cs
+++ b/Facepunch.Steamworks/SteamNative/SteamNative.SteamInventory.cs
@@ -243,6 +243,7 @@ public CallbackHandle RequestEligiblePromoItemDefinitionsIDs( CSteamID steamID /
 			callback = platform.ISteamInventory_RequestEligiblePromoItemDefinitionsIDs( steamID.Value );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return SteamInventoryEligiblePromoItemDefIDs_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -254,6 +255,7 @@ public CallbackHandle RequestPrices( Action<SteamInventoryRequestPricesResult_t,
 			callback = platform.ISteamInventory_RequestPrices();
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return SteamInventoryRequestPricesResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -301,6 +303,7 @@ public CallbackHandle StartPurchase( SteamItemDef_t[] pArrayItemDefs /*const Ste
 			callback = platform.ISteamInventory_StartPurchase( pArrayItemDefs.Select( x => x.Value ).ToArray(), punArrayQuantity, unArrayLength );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return SteamInventoryStartPurchaseResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
diff --git a/Facepunch.Steamworks/SteamNative/SteamNative.SteamMatchmaking.cs b/Facepunch.Steamworks/SteamNative/SteamNative.SteamMatchmaking.cs
index 97c80e2..da740fe 100644
--- a/Facepunch.Steamworks/SteamNative/SteamNative.SteamMatchmaking.cs
+++ b/Facepunch.Steamworks/SteamNative/SteamNative.SteamMatchmaking.cs
@@ -98,6 +98,7 @@ public CallbackHandle CreateLobby( LobbyType eLobbyType /*ELobbyType*/, int cMax
 			callback = platform.ISteamMatchmaking_CreateLobby( eLobbyType, cMaxMembers );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return LobbyCreated_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -219,6 +220,7 @@ public CallbackHandle JoinLobby( CSteamID steamIDLobby /*class CSteamID*/, Actio
 			callback = platform.ISteamMatchmaking_JoinLobby( steamIDLobby.Value );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return LobbyEnter_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -248,6 +250,7 @@ public CallbackHandle RequestLobbyList( Action<LobbyMatchList_t, bool> CallbackF
 			callback = platform.ISteamMatchmaking_RequestLobbyList();
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return LobbyMatchList_t.CallResult( steamworks, callback, CallbackFunction );
 		}
diff --git a/Facepunch.Steamworks/SteamNative/SteamNative.SteamRemoteStorage.cs b/Facepunch.Steamworks/SteamNative/SteamNative.SteamRemoteStorage.cs
index 8493623..22de4be 100644
--- a/Facepunch.Steamworks/SteamNative/SteamNative.SteamRemoteStorage.cs
+++ b/Facepunch.Steamworks/SteamNative/SteamNative.SteamRemoteStorage.cs
@@ -50,6 +50,7 @@ public CallbackHandle CommitPublishedFileUpdate( PublishedFileUpdateHandle_t upd
 			callback = platform.ISteamRemoteStorage_CommitPublishedFileUpdate( updateHandle.Value );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return RemoteStorageUpdatePublishedFileResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -67,6 +68,7 @@ public CallbackHandle DeletePublishedFile( PublishedFileId_t unPublishedFileId /
 			callback = platform.ISteamRemoteStorage_DeletePublishedFile( unPublishedFileId.Value );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return RemoteStorageDeletePublishedFileResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -78,6 +80,7 @@ public CallbackHandle EnumeratePublishedFilesByUserAction( WorkshopFileAction eA
 			callback = platform.ISteamRemoteStorage_EnumeratePublishedFilesByUserAction( eAction, unStartIndex );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return RemoteStorageEnumeratePublishedFilesByUserActionResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -115,6 +118,7 @@ public CallbackHandle EnumeratePublishedWorkshopFiles( WorkshopEnumerationType e
 			}
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return RemoteStorageEnumerateWorkshopFilesResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -126,6 +130,7 @@ public CallbackHandle EnumerateUserPublishedFiles( uint unStartIndex /*uint32*/,
 			callback = platform.ISteamRemoteStorage_EnumerateUserPublishedFiles( unStartIndex );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return RemoteStorageEnumerateUserPublishedFilesResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -163,6 +168,7 @@ public CallbackHandle EnumerateUserSharedWorkshopFiles( CSteamID steamId /*class
 			}
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return RemoteStorageEnumerateUserPublishedFilesResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -174,6 +180,7 @@ public CallbackHandle EnumerateUserSubscribedFiles( uint unStartIndex /*uint32*/
 			callback = platform.ISteamRemoteStorage_EnumerateUserSubscribedFiles( unStartIndex );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return RemoteStorageEnumerateUserSubscribedFilesResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -215,6 +222,7 @@ public CallbackHandle FileReadAsync( string pchFile /*const char **/, uint nOffs
 			callback = platform.ISteamRemoteStorage_FileReadAsync( pchFile, nOffset, cubToRead );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return RemoteStorageFileReadAsyncComplete_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -232,6 +240,7 @@ public CallbackHandle FileShare( string pchFile /*const char **/, Action<RemoteS
 			callback = platform.ISteamRemoteStorage_FileShare( pchFile );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return RemoteStorageFileShareResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -249,6 +258,7 @@ public CallbackHandle FileWriteAsync( string pchFile /*const char **/, IntPtr pv
 			callback = platform.ISteamRemoteStorage_FileWriteAsync( pchFile, (IntPtr) pvData, cubData );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return RemoteStorageFileWriteAsyncComplete_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -323,6 +333,7 @@ public CallbackHandle GetPublishedFileDetails( PublishedFileId_t unPublishedFile
 			callback = platform.ISteamRemoteStorage_GetPublishedFileDetails( unPublishedFileId.Value, unMaxSecondsOld );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return RemoteStorageGetPublishedFileDetailsResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -334,6 +345,7 @@ public CallbackHandle GetPublishedItemVoteDetails( PublishedFileId_t unPublished
 			callback = platform.ISteamRemoteStorage_GetPublishedItemVoteDetails( unPublishedFileId.Value );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return RemoteStorageGetPublishedItemVoteDetailsResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -377,6 +389,7 @@ public CallbackHandle GetUserPublishedItemVoteDetails( PublishedFileId_t unPubli
 			callback = platform.ISteamRemoteStorage_GetUserPublishedItemVoteDetails( unPublishedFileId.Value );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return RemoteStorageGetPublishedItemVoteDetailsResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -426,6 +439,7 @@ public CallbackHandle PublishVideo( WorkshopVideoProvider eVideoProvider /*EWork
 			}
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return RemoteStoragePublishFileProgress_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -463,6 +477,7 @@ public CallbackHandle PublishWorkshopFile( string pchFile /*const char **/, stri
 			}
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return RemoteStoragePublishFileProgress_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -486,6 +501,7 @@ public CallbackHandle SetUserPublishedFileAction( PublishedFileId_t unPublishedF
 			callback = platform.ISteamRemoteStorage_SetUserPublishedFileAction( unPublishedFileId.Value, eAction );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return RemoteStorageSetUserPublishedFileActionResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -497,6 +513,7 @@ public CallbackHandle SubscribePublishedFile( PublishedFileId_t unPublishedFileI
 			callback = platform.ISteamRemoteStorage_SubscribePublishedFile( unPublishedFileId.Value );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return RemoteStorageSubscribePublishedFileResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -508,6 +525,7 @@ public CallbackHandle UGCDownload( UGCHandle_t hContent /*UGCHandle_t*/, uint un
 			callback = platform.ISteamRemoteStorage_UGCDownload( hContent.Value, unPriority );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return RemoteStorageDownloadUGCResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -519,6 +537,7 @@ public CallbackHandle UGCDownloadToLocation( UGCHandle_t hContent /*UGCHandle_t*
 			callback = platform.ISteamRemoteStorage_UGCDownloadToLocation( hContent.Value, pchLocation, unPriority );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return RemoteStorageDownloadUGCResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -536,6 +555,7 @@ public CallbackHandle UnsubscribePublishedFile( PublishedFileId_t unPublishedFil
 			callback = platform.ISteamRemoteStorage_UnsubscribePublishedFile( unPublishedFileId.Value );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return RemoteStorageUnsubscribePublishedFileResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -615,6 +635,7 @@ public CallbackHandle UpdateUserPublishedItemVote( PublishedFileId_t unPublished
 			callback = platform.ISteamRemoteStorage_UpdateUserPublishedItemVote( unPublishedFileId.Value, bVoteUp );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return RemoteStorageUpdateUserPublishedItemVoteResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
diff --git a/Facepunch.Steamworks/SteamNative/SteamNative.SteamUGC.cs b/Facepunch.Steamworks/SteamNative/SteamNative.SteamUGC.cs
index 7d6edf9..eb9dad7 100644
--- a/Facepunch.Steamworks/SteamNative/SteamNative.SteamUGC.cs
+++ b/Facepunch.Steamworks/SteamNative/SteamNative.SteamUGC.cs
@@ -50,6 +50,7 @@ public CallbackHandle AddAppDependency( PublishedFileId_t nPublishedFileID /*Pub
 			callback = platform.ISteamUGC_AddAppDependency( nPublishedFileID.Value, nAppID.Value );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return AddAppDependencyResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -61,6 +62,7 @@ public CallbackHandle AddDependency( PublishedFileId_t nParentPublishedFileID /*
 			callback = platform.ISteamUGC_AddDependency( nParentPublishedFileID.Value, nChildPublishedFileID.Value );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return AddUGCDependencyResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -96,6 +98,7 @@ public CallbackHandle AddItemToFavorites( AppId_t nAppId /*AppId_t*/, PublishedF
 			callback = platform.ISteamUGC_AddItemToFavorites( nAppId.Value, nPublishedFileID.Value );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return UserFavoriteItemsListChanged_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -125,6 +128,7 @@ public CallbackHandle CreateItem( AppId_t nConsumerAppId /*AppId_t*/, WorkshopFi
 			callback = platform.ISteamUGC_CreateItem( nConsumerAppId.Value, eFileType );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return CreateItemResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -159,6 +163,7 @@ public CallbackHandle DeleteItem( PublishedFileId_t nPublishedFileID /*Published
 			callback = platform.ISteamUGC_DeleteItem( nPublishedFileID.Value );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return DeleteItemResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -176,6 +181,7 @@ public CallbackHandle GetAppDependencies( PublishedFileId_t nPublishedFileID /*P
 			callback = platform.ISteamUGC_GetAppDependencies( nPublishedFileID.Value );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return GetAppDependenciesResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -329,6 +335,7 @@ public CallbackHandle GetUserItemVote( PublishedFileId_t nPublishedFileID /*Publ
 			callback = platform.ISteamUGC_GetUserItemVote( nPublishedFileID.Value );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return GetUserItemVoteResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -346,6 +353,7 @@ public CallbackHandle RemoveAppDependency( PublishedFileId_t nPublishedFileID /*
 			callback = platform.ISteamUGC_RemoveAppDependency( nPublishedFileID.Value, nAppID.Value );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return RemoveAppDependencyResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -357,6 +365,7 @@ public CallbackHandle RemoveDependency( PublishedFileId_t nParentPublishedFileID
 			callback = platform.ISteamUGC_RemoveDependency( nParentPublishedFileID.Value, nChildPublishedFileID.Value );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return RemoveUGCDependencyResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -368,6 +377,7 @@ public CallbackHandle RemoveItemFromFavorites( AppId_t nAppId /*AppId_t*/, Publi
 			callback = platform.ISteamUGC_RemoveItemFromFavorites( nAppId.Value, nPublishedFileID.Value );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return UserFavoriteItemsListChanged_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -397,6 +407,7 @@ public CallbackHandle SendQueryUGCRequest( UGCQueryHandle_t handle /*UGCQueryHan
 			callback = platform.ISteamUGC_SendQueryUGCRequest( handle.Value );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return SteamUGCQueryCompleted_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -566,6 +577,7 @@ public CallbackHandle SetUserItemVote( PublishedFileId_t nPublishedFileID /*Publ
 			callback = platform.ISteamUGC_SetUserItemVote( nPublishedFileID.Value, bVoteUp );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return SetUserItemVoteResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -588,6 +600,7 @@ public CallbackHandle StartPlaytimeTracking( PublishedFileId_t[] pvecPublishedFi
 			}
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return StartPlaytimeTrackingResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -604,6 +617,7 @@ public CallbackHandle StopPlaytimeTracking( PublishedFileId_t[] pvecPublishedFil
 			}
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return StopPlaytimeTrackingResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -615,6 +629,7 @@ public CallbackHandle StopPlaytimeTrackingForAllItems( Action<StopPlaytimeTracki
 			callback = platform.ISteamUGC_StopPlaytimeTrackingForAllItems();
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return StopPlaytimeTrackingResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -626,6 +641,7 @@ public CallbackHandle SubmitItemUpdate( UGCUpdateHandle_t handle /*UGCUpdateHand
 			callback = platform.ISteamUGC_SubmitItemUpdate( handle.Value, pchChangeNote );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return SubmitItemUpdateResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -637,6 +653,7 @@ public CallbackHandle SubscribeItem( PublishedFileId_t nPublishedFileID /*Publis
 			callback = platform.ISteamUGC_SubscribeItem( nPublishedFileID.Value );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return RemoteStorageSubscribePublishedFileResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -654,6 +671,7 @@ public CallbackHandle UnsubscribeItem( PublishedFileId_t nPublishedFileID /*Publ
 			callback = platform.ISteamUGC_UnsubscribeItem( nPublishedFileID.Value );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return RemoteStorageUnsubscribePublishedFileResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
diff --git a/Facepunch.Steamworks/SteamNative/SteamNative.SteamUser.cs b/Facepunch.Steamworks/SteamNative/SteamNative.SteamUser.cs
index 91d8b4e..443cee6 100644
--- a/Facepunch.Steamworks/SteamNative/SteamNative.SteamUser.cs
+++ b/Facepunch.Steamworks/SteamNative/SteamNative.SteamUser.cs
@@ -188,6 +188,7 @@ public CallbackHandle RequestEncryptedAppTicket( IntPtr pDataToInclude /*void **
 			callback = platform.ISteamUser_RequestEncryptedAppTicket( (IntPtr) pDataToInclude, cbDataToInclude );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return EncryptedAppTicketResponse_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -199,6 +200,7 @@ public CallbackHandle RequestStoreAuthURL( string pchRedirectURL /*const char **
 			callback = platform.ISteamUser_RequestStoreAuthURL( pchRedirectURL );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return StoreAuthURLResponse_t.CallResult( steamworks, callback, CallbackFunction );
 		}
diff --git a/Facepunch.Steamworks/SteamNative/SteamNative.SteamUserStats.cs b/Facepunch.Steamworks/SteamNative/SteamNative.SteamUserStats.cs
index 201a82b..c7c3e16 100644
--- a/Facepunch.Steamworks/SteamNative/SteamNative.SteamUserStats.cs
+++ b/Facepunch.Steamworks/SteamNative/SteamNative.SteamUserStats.cs
@@ -50,6 +50,7 @@ public CallbackHandle AttachLeaderboardUGC( SteamLeaderboard_t hSteamLeaderboard
 			callback = platform.ISteamUserStats_AttachLeaderboardUGC( hSteamLeaderboard.Value, hUGC.Value );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return LeaderboardUGCSet_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -67,6 +68,7 @@ public CallbackHandle DownloadLeaderboardEntries( SteamLeaderboard_t hSteamLeade
 			callback = platform.ISteamUserStats_DownloadLeaderboardEntries( hSteamLeaderboard.Value, eLeaderboardDataRequest, nRangeStart, nRangeEnd );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return LeaderboardScoresDownloaded_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -78,6 +80,7 @@ public CallbackHandle DownloadLeaderboardEntriesForUsers( SteamLeaderboard_t hSt
 			callback = platform.ISteamUserStats_DownloadLeaderboardEntriesForUsers( hSteamLeaderboard.Value, (IntPtr) prgUsers, cUsers );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return LeaderboardScoresDownloaded_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -89,6 +92,7 @@ public CallbackHandle FindLeaderboard( string pchLeaderboardName /*const char **
 			callback = platform.ISteamUserStats_FindLeaderboard( pchLeaderboardName );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return LeaderboardFindResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -100,6 +104,7 @@ public CallbackHandle FindOrCreateLeaderboard( string pchLeaderboardName /*const
 			callback = platform.ISteamUserStats_FindOrCreateLeaderboard( pchLeaderboardName, eLeaderboardSortMethod, eLeaderboardDisplayType );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return LeaderboardFindResult_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -244,6 +249,7 @@ public CallbackHandle GetNumberOfCurrentPlayers( Action<NumberOfCurrentPlayers_t
 			callback = platform.ISteamUserStats_GetNumberOfCurrentPlayers();
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return NumberOfCurrentPlayers_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -303,6 +309,7 @@ public CallbackHandle RequestGlobalAchievementPercentages( Action<GlobalAchievem
 			callback = platform.ISteamUserStats_RequestGlobalAchievementPercentages();
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return GlobalAchievementPercentagesReady_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -314,6 +321,7 @@ public CallbackHandle RequestGlobalStats( int nHistoryDays /*int*/, Action<Globa
 			callback = platform.ISteamUserStats_RequestGlobalStats( nHistoryDays );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return GlobalStatsReceived_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -325,6 +333,7 @@ public CallbackHandle RequestUserStats( CSteamID steamIDUser /*class CSteamID*/,
 			callback = platform.ISteamUserStats_RequestUserStats( steamIDUser.Value );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return UserStatsReceived_t.CallResult( steamworks, callback, CallbackFunction );
 		}
@@ -372,6 +381,7 @@ public CallbackHandle UploadLeaderboardScore( SteamLeaderboard_t hSteamLeaderboa
 			callback = platform.ISteamUserStats_UploadLeaderboardScore( hSteamLeaderboard.Value, eLeaderboardUploadScoreMethod, nScore, pScoreDetails, cScoreDetailsCount );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return LeaderboardScoreUploaded_t.CallResult( steamworks, callback, CallbackFunction );
 		}
diff --git a/Facepunch.Steamworks/SteamNative/SteamNative.SteamUtils.cs b/Facepunch.Steamworks/SteamNative/SteamNative.SteamUtils.cs
index 76f224d..dec7642 100644
--- a/Facepunch.Steamworks/SteamNative/SteamNative.SteamUtils.cs
+++ b/Facepunch.Steamworks/SteamNative/SteamNative.SteamUtils.cs
@@ -56,6 +56,7 @@ public CallbackHandle CheckFileSignature( string szFileName /*const char **/, Ac
 			callback = platform.ISteamUtils_CheckFileSignature( szFileName );
 			
 			if ( CallbackFunction == null ) return null;
+			if ( callback == 0 ) return null;
 			
 			return CheckFileSignature_t.CallResult( steamworks, callback, CallbackFunction );
 		}
diff --git a/Generator/CodeWriter/Class.cs b/Generator/CodeWriter/Class.cs
index df76dbc..896a5fd 100644
--- a/Generator/CodeWriter/Class.cs
+++ b/Generator/CodeWriter/Class.cs
@@ -175,6 +175,7 @@ private void Detect_CallResult( List<Argument> argList, List<Argument> callargs
 
             AfterLines.Add( "" );
             AfterLines.Add( "if ( CallbackFunction == null ) return null;" );
+            AfterLines.Add("if ( callback == 0 ) return null;");
             AfterLines.Add( "" );
 
             AfterLines.Add( $"return {MethodDef.CallResult}.CallResult( steamworks, callback, CallbackFunction );" );