diff --git a/src/scripting/types.cpp b/src/scripting/types.cpp
index f07356d42..91ceb9077 100644
--- a/src/scripting/types.cpp
+++ b/src/scripting/types.cpp
@@ -2247,6 +2247,7 @@ bool PStruct::ReadValue(FSerializer &ar, const char *key, void *addr) const
 
 PField *PStruct::AddField(FName name, PType *type, uint32_t flags)
 {
+	assert(type->Size > 0);
 	return Symbols.AddField(name, type, flags, Size, &Align);
 }
 
diff --git a/src/scripting/zscript/zcc_compile.cpp b/src/scripting/zscript/zcc_compile.cpp
index 5d42d64ba..71f8e6d35 100644
--- a/src/scripting/zscript/zcc_compile.cpp
+++ b/src/scripting/zscript/zcc_compile.cpp
@@ -1298,6 +1298,11 @@ bool ZCCCompiler::CompileFields(PContainerType *type, TArray<ZCC_VarDeclarator *
 		auto name = field->Names;
 		do
 		{
+			if (fieldtype->Size == 0 && !(varflags & VARF_Native))	// Size not known yet.
+			{
+				return false;
+			}
+
 			if (AddTreeNode(name->Name, name, TreeNodes, !forstruct))
 			{
 				auto thisfieldtype = fieldtype;