diff --git a/src/d_main.cpp b/src/d_main.cpp
index 72be3815ab..2670221c09 100644
--- a/src/d_main.cpp
+++ b/src/d_main.cpp
@@ -2514,6 +2514,9 @@ void D_DoomMain (void)
 
 		// Create replacements for dehacked pickups
 		FinishDehPatch();
+		
+		// clean up the compiler symbols which are not needed any longer.
+		RemoveUnusedSymbols();
 
 		InitActorNumsFromMapinfo();
 		InitSpawnablesFromMapinfo();
diff --git a/src/dobjtype.cpp b/src/dobjtype.cpp
index dbd3e6d6fd..76330867e7 100644
--- a/src/dobjtype.cpp
+++ b/src/dobjtype.cpp
@@ -3898,3 +3898,45 @@ void FNamespaceManager::ReleaseSymbols()
 	GlobalNamespace = nullptr;
 	AllNamespaces.Clear();
 }
+
+// removes all symbols from the symbol tables.
+// After running the compiler these are not needed anymore.
+// Only the namespaces themselves are kept because the type table references them.
+int FNamespaceManager::RemoveSymbols()
+{
+	int count = 0;
+	for (auto ns : AllNamespaces)
+	{
+		count += ns->Symbols.Symbols.CountUsed();
+		ns->Symbols.ReleaseSymbols();
+	}
+	return count;
+}
+
+void RemoveUnusedSymbols()
+{
+	// Global symbols are not needed anymore after running the compiler.
+	int count = Namespaces.RemoveSymbols();
+
+	// We do not need any non-field and non-function symbols in structs and classes anymore.
+	for (size_t i = 0; i < countof(TypeTable.TypeHash); ++i)
+	{
+		for (PType *ty = TypeTable.TypeHash[i]; ty != NULL; ty = ty->HashNext)
+		{
+			if (ty->IsKindOf(RUNTIME_CLASS(PStruct)))
+			{
+				auto it = ty->Symbols.GetIterator();
+				PSymbolTable::MapType::Pair *pair;
+				while (it.NextPair(pair))
+				{
+					if (!pair->Value->IsKindOf(RUNTIME_CLASS(PField)) && !pair->Value->IsKindOf(RUNTIME_CLASS(PFunction)))
+					{
+						ty->Symbols.RemoveSymbol(pair->Value);
+						count++;
+					}
+				}
+			}
+		}
+	}
+	DPrintf(DMSG_SPAMMY, "%d symbols removed after compilation\n", count);
+}
diff --git a/src/dobjtype.h b/src/dobjtype.h
index 61747134cc..632ef96bbd 100644
--- a/src/dobjtype.h
+++ b/src/dobjtype.h
@@ -76,6 +76,7 @@ class VMFrameStack;
 struct VMValue;
 struct VMReturn;
 class VMFunction;
+struct FNamespaceManager;
 
 // A VM function ------------------------------------------------------------
 
@@ -157,6 +158,7 @@ private:
 	MapType Symbols;
 
 	friend class DObject;
+	friend struct FNamespaceManager;
 };
 
 // A symbol for a compiler tree node ----------------------------------------
@@ -1010,6 +1012,7 @@ struct FNamespaceManager
 	PNamespace *NewNamespace(int filenum);
 	size_t MarkSymbols();
 	void ReleaseSymbols();
+	int RemoveSymbols();
 };
 
 extern FNamespaceManager Namespaces;
@@ -1047,4 +1050,7 @@ inline T *&DObject::PointerVar(FName field)
 {
 	return *(T**)ScriptVar(field, nullptr);	// pointer check is more tricky and for the handful of uses in the DECORATE parser not worth the hassle.
 }
+
+void RemoveUnusedSymbols();
+
 #endif
diff --git a/src/p_acs.cpp b/src/p_acs.cpp
index 50f50ff31c..24142e0ec5 100644
--- a/src/p_acs.cpp
+++ b/src/p_acs.cpp
@@ -9716,7 +9716,16 @@ scriptwait:
 
 	if (runaway != 0 && InModuleScriptNumber >= 0)
 	{
-		activeBehavior->GetScriptPtr(InModuleScriptNumber)->ProfileData.AddRun(runaway);
+		auto scriptptr = activeBehavior->GetScriptPtr(InModuleScriptNumber);
+		if (scriptptr != nullptr)
+		{
+			scriptptr->ProfileData.AddRun(runaway);
+		}
+		else
+		{
+			// It is pointless to continue execution. The script is broken and needs to be aborted.
+			I_Error("Bad script definition encountered. Script %d is reported running but not present.\nThe most likely cause for this message is using 'delay' inside a function which is not supported.\nPlease check the ACS compiler used for compiling the script!", InModuleScriptNumber);
+		}
 	}
 
 	if (state == SCRIPT_DivideBy0)
diff --git a/src/scripting/codegeneration/codegen.cpp b/src/scripting/codegeneration/codegen.cpp
index 1d16b182ff..d090fa6e42 100644
--- a/src/scripting/codegeneration/codegen.cpp
+++ b/src/scripting/codegeneration/codegen.cpp
@@ -1613,7 +1613,7 @@ FxExpression *FxTypeCast::Resolve(FCompileContext &ctx)
 	}
 	else if (ValueType->IsKindOf(RUNTIME_CLASS(PClassPointer)))
 	{
-		FxExpression *x = new FxClassTypeCast(static_cast<PClassPointer*>(ValueType), basex);
+		FxExpression *x = new FxClassTypeCast(static_cast<PClassPointer*>(ValueType), basex, Explicit);
 		x = x->Resolve(ctx);
 		basex = nullptr;
 		delete this;
@@ -4412,7 +4412,7 @@ FxExpression *FxTypeCheck::Resolve(FCompileContext& ctx)
 
 	if (left->ValueType->IsKindOf(RUNTIME_CLASS(PClassPointer)))
 	{
-		left = new FxClassTypeCast(NewClassPointer(RUNTIME_CLASS(DObject)), left);
+		left = new FxClassTypeCast(NewClassPointer(RUNTIME_CLASS(DObject)), left, false);
 		ClassCheck = true;
 	}
 	else
@@ -4420,7 +4420,7 @@ FxExpression *FxTypeCheck::Resolve(FCompileContext& ctx)
 		left = new FxTypeCast(left, NewPointer(RUNTIME_CLASS(DObject)), false);
 		ClassCheck = false;
 	}
-	right = new FxClassTypeCast(NewClassPointer(RUNTIME_CLASS(DObject)), right);
+	right = new FxClassTypeCast(NewClassPointer(RUNTIME_CLASS(DObject)), right, false);
 
 	RESOLVE(left, ctx);
 	RESOLVE(right, ctx);
@@ -9922,12 +9922,13 @@ VMFunction *FxReturnStatement::GetDirectFunction()
 //
 //==========================================================================
 
-FxClassTypeCast::FxClassTypeCast(PClassPointer *dtype, FxExpression *x)
+FxClassTypeCast::FxClassTypeCast(PClassPointer *dtype, FxExpression *x, bool explicitily)
 : FxExpression(EFX_ClassTypeCast, x->ScriptPosition)
 {
 	ValueType = dtype;
 	desttype = dtype->ClassRestriction;
 	basex=x;
+	Explicit = explicitily;
 }
 
 //==========================================================================
@@ -9991,7 +9992,9 @@ FxExpression *FxClassTypeCast::Resolve(FCompileContext &ctx)
 
 		if (clsname != NAME_None)
 		{
-			cls = FindClassType(clsname, ctx);
+			if (Explicit) cls = FindClassType(clsname, ctx);
+			else cls = PClass::FindClass(clsname);
+			
 			if (cls == nullptr)
 			{
 				/* lax */
@@ -10141,7 +10144,7 @@ FxExpression *FxClassPtrCast::Resolve(FCompileContext &ctx)
 	}
 	else if (basex->ValueType == TypeString || basex->ValueType == TypeName)
 	{
-		FxExpression *x = new FxClassTypeCast(to, basex);
+		FxExpression *x = new FxClassTypeCast(to, basex, true);
 		basex = nullptr;
 		delete this;
 		return x->Resolve(ctx);
diff --git a/src/scripting/codegeneration/codegen.h b/src/scripting/codegeneration/codegen.h
index 7c18589c51..42d5b0ccfd 100644
--- a/src/scripting/codegeneration/codegen.h
+++ b/src/scripting/codegeneration/codegen.h
@@ -1913,10 +1913,11 @@ class FxClassTypeCast : public FxExpression
 {
 	PClass *desttype;
 	FxExpression *basex;
+	bool Explicit;
 
 public:
 
-	FxClassTypeCast(PClassPointer *dtype, FxExpression *x);
+	FxClassTypeCast(PClassPointer *dtype, FxExpression *x, bool explicitly);
 	~FxClassTypeCast();
 	FxExpression *Resolve(FCompileContext&);
 	ExpEmit Emit(VMFunctionBuilder *build);
diff --git a/src/scripting/decorate/thingdef_parse.cpp b/src/scripting/decorate/thingdef_parse.cpp
index 81ab765f5d..9b78ef3d57 100644
--- a/src/scripting/decorate/thingdef_parse.cpp
+++ b/src/scripting/decorate/thingdef_parse.cpp
@@ -197,7 +197,7 @@ FxExpression *ParseParameter(FScanner &sc, PClassActor *cls, PType *type)
 		sc.SetEscape(true);
 		sc.MustGetString();
 		sc.SetEscape(false);
-		x = new FxClassTypeCast(static_cast<PClassPointer *>(type), new FxConstant(FName(sc.String), sc));
+		x = new FxClassTypeCast(static_cast<PClassPointer *>(type), new FxConstant(FName(sc.String), sc), false);
 	}
 	else
 	{