diff --git a/src/dobjtype.cpp b/src/dobjtype.cpp
index b27546e33..e3dfd232a 100644
--- a/src/dobjtype.cpp
+++ b/src/dobjtype.cpp
@@ -776,16 +776,18 @@ PClass *PClass::FindClassTentative(FName name)
 //
 //==========================================================================
 
-int PClass::FindVirtualIndex(FName name, PPrototype *proto)
+int PClass::FindVirtualIndex(FName name, PFunction::Variant *variant, PFunction *parentfunc)
 {
+	auto proto = variant->Proto;
 	for (unsigned i = 0; i < Virtuals.Size(); i++)
 	{
 		if (Virtuals[i]->Name == name)
 		{
 			auto vproto = Virtuals[i]->Proto;
 			if (vproto->ReturnTypes.Size() != proto->ReturnTypes.Size() ||
-				vproto->ArgumentTypes.Size() != proto->ArgumentTypes.Size())
+				vproto->ArgumentTypes.Size() < proto->ArgumentTypes.Size())
 			{
+
 				continue;	// number of parameters does not match, so it's incompatible
 			}
 			bool fail = false;
@@ -808,7 +810,26 @@ int PClass::FindVirtualIndex(FName name, PPrototype *proto)
 					break;
 				}
 			}
-			if (!fail) return i;
+			if (!fail)
+			{
+				if (vproto->ArgumentTypes.Size() > proto->ArgumentTypes.Size() && parentfunc)
+				{
+					// Check if the difference between both functions is only some optional arguments.
+					for (unsigned a = proto->ArgumentTypes.Size(); a < vproto->ArgumentTypes.Size(); a++)
+					{
+						if (!(parentfunc->Variants[0].ArgFlags[a] & VARF_Optional)) return -1;
+					}
+
+					// Todo: extend the prototype
+					for (unsigned a = proto->ArgumentTypes.Size(); a < vproto->ArgumentTypes.Size(); a++)
+					{
+						proto->ArgumentTypes.Push(vproto->ArgumentTypes[a]);
+						variant->ArgFlags.Push(parentfunc->Variants[0].ArgFlags[a]);
+						variant->ArgNames.Push(NAME_None);
+					}
+				}
+				return i;
+			}
 		}
 	}
 	return -1;
diff --git a/src/dobjtype.h b/src/dobjtype.h
index 12a6ae287..212174005 100644
--- a/src/dobjtype.h
+++ b/src/dobjtype.h
@@ -42,7 +42,7 @@ public:
 	void WriteAllFields(FSerializer &ar, const void *addr) const;
 	bool ReadAllFields(FSerializer &ar, void *addr) const;
 	void InitializeDefaults();
-	int FindVirtualIndex(FName name, PPrototype *proto);
+	int FindVirtualIndex(FName name, PFunction::Variant *variant, PFunction *parentfunc);
 	PSymbol *FindSymbol(FName symname, bool searchparents) const;
 	PField *AddField(FName name, PType *type, uint32_t flags);
 
diff --git a/src/scripting/zscript/zcc_compile.cpp b/src/scripting/zscript/zcc_compile.cpp
index cc8424b50..0a06f7b7c 100644
--- a/src/scripting/zscript/zcc_compile.cpp
+++ b/src/scripting/zscript/zcc_compile.cpp
@@ -2694,7 +2694,9 @@ void ZCCCompiler::CompileFunction(ZCC_StructWork *c, ZCC_FuncDeclarator *f, bool
 
 			if (forclass)
 			{
-				int vindex = clstype->FindVirtualIndex(sym->SymbolName, sym->Variants[0].Proto);
+				auto parentfunc = clstype->ParentClass? dyn_cast<PFunction>(clstype->ParentClass->VMType->Symbols.FindSymbol(sym->SymbolName, true)) : nullptr;
+
+				int vindex = clstype->FindVirtualIndex(sym->SymbolName, &sym->Variants[0], parentfunc);
 				// specifying 'override' is necessary to prevent one of the biggest problem spots with virtual inheritance: Mismatching argument types.
 				if (varflags & VARF_Override)
 				{
@@ -2705,7 +2707,6 @@ void ZCCCompiler::CompileFunction(ZCC_StructWork *c, ZCC_FuncDeclarator *f, bool
 					else
 					{
 						auto oldfunc = clstype->Virtuals[vindex];
-						auto parentfunc = dyn_cast<PFunction>(clstype->ParentClass->VMType->Symbols.FindSymbol(sym->SymbolName, true));
 						if (parentfunc && parentfunc->mVersion > mVersion)
 						{
 							Error(f, "Attempt to override function %s which is incompatible with version %d.%d.%d", FName(f->Name).GetChars(), mVersion.major, mVersion.minor, mVersion.revision);
@@ -2765,7 +2766,7 @@ void ZCCCompiler::CompileFunction(ZCC_StructWork *c, ZCC_FuncDeclarator *f, bool
 		}
 		else if (forclass)
 		{
-			int vindex = clstype->FindVirtualIndex(sym->SymbolName, sym->Variants[0].Proto);
+			int vindex = clstype->FindVirtualIndex(sym->SymbolName, &sym->Variants[0], nullptr);
 			if (vindex != -1)
 			{
 				Error(f, "Function %s attempts to override parent function without 'override' qualifier", FName(f->Name).GetChars());