diff --git a/flytekit/core/type_engine.py b/flytekit/core/type_engine.py
index 123cb4a0ef..f79ddc3082 100644
--- a/flytekit/core/type_engine.py
+++ b/flytekit/core/type_engine.py
@@ -1445,6 +1445,7 @@ def to_literal(self, ctx: FlyteContext, python_val: T, python_type: Type[T], exp
         python_type = get_underlying_type(python_type)
 
         found_res = False
+        is_ambiguous = False
         res = None
         res_type = None
         for i in range(len(get_args(python_type))):
@@ -1454,13 +1455,15 @@ def to_literal(self, ctx: FlyteContext, python_val: T, python_type: Type[T], exp
                 res = trans.to_literal(ctx, python_val, t, expected.union_type.variants[i])
                 res_type = _add_tag_to_type(trans.get_literal_type(t), trans.name)
                 if found_res:
-                    # Should really never happen, sanity check
-                    raise TypeError("Ambiguous choice of variant for union type")
+                    is_ambiguous = True
                 found_res = True
-            except (TypeTransformerFailedError, AttributeError, ValueError, AssertionError) as e:
+            except Exception as e:
                 logger.debug(f"Failed to convert from {python_val} to {t}", e)
                 continue
 
+        if is_ambiguous:
+            raise TypeError("Ambiguous choice of variant for union type")
+
         if found_res:
             return Literal(scalar=Scalar(union=Union(value=res, stored_type=res_type)))
 
@@ -1477,6 +1480,8 @@ def to_python_value(self, ctx: FlyteContext, lv: Literal, expected_python_type:
                 union_tag = union_type.structure.tag
 
         found_res = False
+        is_ambiguous = False
+        cur_transformer = ""
         res = None
         res_tag = None
         for v in get_args(expected_python_type):
@@ -1494,25 +1499,27 @@ def to_python_value(self, ctx: FlyteContext, lv: Literal, expected_python_type:
                     assert lv.scalar.union is not None  # type checker
 
                     res = trans.to_python_value(ctx, lv.scalar.union.value, v)
-                    res_tag = trans.name
                     if found_res:
-                        raise TypeError(
-                            "Ambiguous choice of variant for union type. "
-                            + f"Both {res_tag} and {trans.name} transformers match"
-                        )
-                    found_res = True
+                        is_ambiguous = True
+                        cur_transformer = trans.name
+                        break
                 else:
                     res = trans.to_python_value(ctx, lv, v)
                     if found_res:
-                        raise TypeError(
-                            "Ambiguous choice of variant for union type. "
-                            + f"Both {res_tag} and {trans.name} transformers match"
-                        )
-                    res_tag = trans.name
-                    found_res = True
-            except (TypeTransformerFailedError, AttributeError) as e:
+                        is_ambiguous = True
+                        cur_transformer = trans.name
+                        break
+                res_tag = trans.name
+                found_res = True
+            except Exception as e:
                 logger.debug(f"Failed to convert from {lv} to {v}", e)
 
+        if is_ambiguous:
+            raise TypeError(
+                "Ambiguous choice of variant for union type. "
+                + f"Both {res_tag} and {cur_transformer} transformers match"
+            )
+
         if found_res:
             return res
 
diff --git a/tests/flytekit/unit/core/test_type_engine.py b/tests/flytekit/unit/core/test_type_engine.py
index 227be2d0ff..3ce3570b49 100644
--- a/tests/flytekit/unit/core/test_type_engine.py
+++ b/tests/flytekit/unit/core/test_type_engine.py
@@ -2034,6 +2034,20 @@ def test_schema_in_dataclass():
     assert o == ot
 
 
+def test_union_in_dataclass():
+    schema = TestSchema()
+    df = pd.DataFrame(data={"some_str": ["a", "b", "c"]})
+    schema.open().write(df)
+    o = Result(result=InnerResult(number=1, schema=schema), schema=schema)
+    ctx = FlyteContext.current_context()
+    tf = UnionTransformer()
+    pt = typing.Union[Result, InnerResult]
+    lt = tf.get_literal_type(pt)
+    lv = tf.to_literal(ctx, o, pt, lt)
+    ot = tf.to_python_value(ctx, lv=lv, expected_python_type=pt)
+    return o == ot
+
+
 @dataclass
 class InnerResult_dataclassjsonmixin(DataClassJSONMixin):
     number: int