diff --git a/Facepunch.Steamworks/SteamClient.cs b/Facepunch.Steamworks/SteamClient.cs
index 49b923b..cee212e 100644
--- a/Facepunch.Steamworks/SteamClient.cs
+++ b/Facepunch.Steamworks/SteamClient.cs
@@ -17,6 +17,9 @@ namespace Steamworks
 		/// </summary>
 		public static void Init( uint appid, bool asyncCallbacks = true )
 		{
+			if ( initialized )
+				throw new System.Exception( "Calling SteamClient.Init but is already initialized" );
+
 			System.Environment.SetEnvironmentVariable( "SteamAppId", appid.ToString() );
 			System.Environment.SetEnvironmentVariable( "SteamGameId", appid.ToString() );
 
diff --git a/Facepunch.Steamworks/SteamServer.cs b/Facepunch.Steamworks/SteamServer.cs
index eca72d8..61a3a80 100644
--- a/Facepunch.Steamworks/SteamServer.cs
+++ b/Facepunch.Steamworks/SteamServer.cs
@@ -61,6 +61,9 @@ namespace Steamworks
 		/// </summary>
 		public static void Init( AppId appid, SteamServerInit init, bool asyncCallbacks = true )
 		{
+			if ( IsValid )
+				throw new System.Exception( "Calling SteamServer.Init but is already initialized" );
+
 			uint ipaddress = 0; // Any Port
 
 			if ( init.SteamPort == 0 )