diff --git a/src/dobjtype.cpp b/src/dobjtype.cpp
index 7877a79db..fdb85a892 100644
--- a/src/dobjtype.cpp
+++ b/src/dobjtype.cpp
@@ -1414,11 +1414,12 @@ PStruct::PStruct(FName name, DObject *outer)
 //
 // PStruct :: AddField
 //
-// Appends a new field to the end of a struct.
+// Appends a new field to the end of a struct. Returns either the new field
+// or NULL if a symbol by that name already exists.
 //
 //==========================================================================
 
-PField *PStruct::AddField(FName name, PType *type)
+PField *PStruct::AddField(FName name, PType *type, DWORD flags)
 {
 	PField *field = new PField(name, type);
 
@@ -1432,8 +1433,12 @@ PField *PStruct::AddField(FName name, PType *type)
 	// its fields.
 	Align = MAX(Align, type->Align);
 
+	if (Symbols.AddSymbol(field) == NULL)
+	{ // name is already in use
+		delete field;
+		return NULL;
+	}
 	Fields.Push(field);
-	Symbols.AddSymbol(field);
 
 	return field;
 }
diff --git a/src/dobjtype.h b/src/dobjtype.h
index c4fdf48b0..0018d38c4 100644
--- a/src/dobjtype.h
+++ b/src/dobjtype.h
@@ -467,7 +467,7 @@ public:
 	TArray<PField *> Fields;
 	PSymbolTable	 Symbols;
 
-	PField *AddField(FName name, PType *type);
+	PField *AddField(FName name, PType *type, DWORD flags=0);
 
 	size_t PropagateMark();
 protected: