diff --git a/sp/src/public/vscript/ivscript.h b/sp/src/public/vscript/ivscript.h
index c0a0cf08..1eba404c 100644
--- a/sp/src/public/vscript/ivscript.h
+++ b/sp/src/public/vscript/ivscript.h
@@ -263,6 +263,8 @@ inline const char * ScriptFieldTypeName( int16 eType)
 
 //---------------------------------------------------------
 
+struct ScriptClassDesc_t;
+
 struct ScriptFuncDescriptor_t
 {
 	ScriptFuncDescriptor_t()
@@ -270,11 +272,13 @@ struct ScriptFuncDescriptor_t
 		m_pszFunction = NULL;
 		m_ReturnType = FIELD_TYPEUNKNOWN;
 		m_pszDescription = NULL;
+		m_pScriptClassDesc = NULL;
 	}
 
 	const char *m_pszScriptName;
 	const char *m_pszFunction;
 	const char *m_pszDescription;
+	ScriptClassDesc_t *m_pScriptClassDesc;
 	ScriptDataType_t m_ReturnType;
 	CUtlVector<ScriptDataType_t> m_Parameters;
 };
diff --git a/sp/src/public/vscript/vscript_templates.h b/sp/src/public/vscript/vscript_templates.h
index 9f2054cc..bda6bc9e 100644
--- a/sp/src/public/vscript/vscript_templates.h
+++ b/sp/src/public/vscript/vscript_templates.h
@@ -61,7 +61,7 @@ FUNC_GENERATE_ALL( DEFINE_MEMBER_FUNC_TYPE_DEDUCER );
 
 FUNC_GENERATE_ALL( DEFINE_CONST_MEMBER_FUNC_TYPE_DEDUCER );
 
-#define ScriptInitMemberFuncDescriptor_( pDesc, class, func, scriptName )	if ( 0 ) {} else { (pDesc)->m_pszScriptName = scriptName; (pDesc)->m_pszFunction = #func; ScriptDeduceFunctionSignature( pDesc, (class *)(0), &class::func ); }
+#define ScriptInitMemberFuncDescriptor_( pDesc, class, func, scriptName )	if ( 0 ) {} else { (pDesc)->m_pszScriptName = scriptName; (pDesc)->m_pszFunction = #func; ScriptDeduceFunctionSignature( pDesc, (class *)(0), &class::func ); (pDesc)->m_pScriptClassDesc = GetScriptDesc<class>(nullptr); }
 
 #define ScriptInitFuncDescriptorNamed( pDesc, func, scriptName )						if ( 0 ) {} else { (pDesc)->m_pszScriptName = scriptName; (pDesc)->m_pszFunction = #func; ScriptDeduceFunctionSignature( pDesc, &func ); }
 #define ScriptInitFuncDescriptor( pDesc, func )											ScriptInitFuncDescriptorNamed( pDesc, func, #func )
diff --git a/sp/src/vscript/vscript_squirrel.cpp b/sp/src/vscript/vscript_squirrel.cpp
index 584402a1..39139fec 100644
--- a/sp/src/vscript/vscript_squirrel.cpp
+++ b/sp/src/vscript/vscript_squirrel.cpp
@@ -1427,18 +1427,30 @@ SQInteger function_stub(HSQUIRRELVM vm)
 
 	if (pFunc->m_flags & SF_MEMBER_FUNC)
 	{
-		SQUserPointer self;
-		if (SQ_FAILED(sq_getinstanceup(vm, 1, &self, 0)))
+		ClassInstanceData* classInstanceData;
+		if (SQ_FAILED(sq_getinstanceup(vm, 1, (SQUserPointer*)&classInstanceData, 0)))
 		{
-			return sq_throwerror(vm, "Expected class userpointer");
+			return SQ_ERROR;
 		}
 
-		if (!self)
+		if (!classInstanceData)
 		{
 			return sq_throwerror(vm, "Accessed null instance");
 		}
 
-		instance = ((ClassInstanceData*)self)->instance;
+		// check that the type of self, or any basetype, matches the function description
+		ScriptClassDesc_t *selfType = classInstanceData->desc;
+		while (selfType != pFunc->m_desc.m_pScriptClassDesc)
+		{
+			if (!selfType)
+			{
+				return sq_throwerror(vm, "Mismatched instance type");
+			}
+			selfType = selfType->m_pBaseDesc;
+			Assert(selfType != classInstanceData->desc); // there should be no infinite loop
+		}
+
+		instance = classInstanceData->instance;
 	}
 
 	ScriptVariant_t script_retval;