diff --git a/include/flatbuffers/idl.h b/include/flatbuffers/idl.h
index d3519e4f1..a28745f0e 100644
--- a/include/flatbuffers/idl.h
+++ b/include/flatbuffers/idl.h
@@ -438,6 +438,10 @@ struct EnumDef : public Definition {
   SymbolTable<EnumVal> vals;
 };
 
+inline bool IsString(const Type &type) {
+  return type.base_type == BASE_TYPE_STRING;
+}
+
 inline bool IsStruct(const Type &type) {
   return type.base_type == BASE_TYPE_STRUCT && type.struct_def->fixed;
 }
diff --git a/src/idl_parser.cpp b/src/idl_parser.cpp
index d2c729a74..b9086840d 100644
--- a/src/idl_parser.cpp
+++ b/src/idl_parser.cpp
@@ -2998,8 +2998,8 @@ CheckedError Parser::ParseRoot(const char *source, const char **include_paths,
       for (auto val_it = enum_def.Vals().begin();
            val_it != enum_def.Vals().end(); ++val_it) {
         auto &val = **val_it;
-        if (!SupportsAdvancedUnionFeatures() && val.union_type.struct_def &&
-            val.union_type.struct_def->fixed)
+        if (!SupportsAdvancedUnionFeatures() &&
+            (IsStruct(val.union_type) || IsString(val.union_type)))
           return Error(
               "only tables can be union elements in the generated language: " +
               val.name);