fixup

Author: TomAugspurger

pandas/core/dtypes/common.py

@@ -700,7 +700,7 @@ def _is_dtype_union_equal(source, target):
     """
     source = _get_dtype(source)
     target = _get_dtype(target)
-    if source == 'category' and target == 'category':
+    if is_categorical_dtype(source) and is_categorical_dtype(target):
         # ordered False for both
         return source.ordered is target.ordered
     else: