diff --git a/bigframes/functions/function_typing.py b/bigframes/functions/function_typing.py
index 44ee071001..ecbc901317 100644
--- a/bigframes/functions/function_typing.py
+++ b/bigframes/functions/function_typing.py
@@ -60,8 +60,21 @@ class UnsupportedTypeError(ValueError):
     def __init__(self, type_, supported_types):
         self.type = type_
         self.supported_types = supported_types
+
+        types_to_format = supported_types
+        if isinstance(supported_types, dict):
+            types_to_format = supported_types.keys()
+
+        supported_types_str = ", ".join(
+            sorted([getattr(t, "__name__", str(t)) for t in types_to_format])
+        )
+        if get_origin(type_) is not None:
+            type_str = str(type_)
+        else:
+            type_str = getattr(type_, "__name__", str(type_))
+
         super().__init__(
-            f"'{type_}' must be one of the supported types ({supported_types}) "
+            f"'{type_str}' must be one of the supported types ({supported_types_str}) "
             "or a list of one of those types."
         )
 
diff --git a/tests/unit/functions/test_function_typing.py b/tests/unit/functions/test_function_typing.py
new file mode 100644
index 0000000000..53e4ca7d4d
--- /dev/null
+++ b/tests/unit/functions/test_function_typing.py
@@ -0,0 +1,68 @@
+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import datetime
+import decimal
+
+import pytest
+
+from bigframes.functions import function_typing
+
+
+def test_unsupported_type_error_init_with_dict():
+    # Arrange
+    unsupported_type = decimal.Decimal
+    supported_types = {int: "INT64", float: "FLOAT64"}
+
+    # Act
+    err = function_typing.UnsupportedTypeError(unsupported_type, supported_types)
+
+    # Assert
+    assert "Decimal" in str(err)
+    assert "float, int" in str(err)
+
+
+def test_unsupported_type_error_init_with_set():
+    # Arrange
+    unsupported_type = decimal.Decimal
+    supported_types = {int, float}
+
+    # Act
+    err = function_typing.UnsupportedTypeError(unsupported_type, supported_types)
+
+    # Assert
+    assert "Decimal" in str(err)
+    assert "float, int" in str(err)
+
+
+def test_sdk_type_from_python_type_raises_unsupported_type_error():
+    # Arrange
+    unsupported_type = datetime.datetime
+
+    # Act & Assert
+    with pytest.raises(function_typing.UnsupportedTypeError) as excinfo:
+        function_typing.sdk_type_from_python_type(unsupported_type)
+    assert "datetime" in str(excinfo.value)
+    assert "bool, bytes, float, int, str" in str(excinfo.value)
+
+
+def test_sdk_type_from_python_type_with_generic_type_raises_unsupported_type_error():
+    # Arrange
+    unsupported_type = list[str]
+
+    # Act & Assert
+    with pytest.raises(function_typing.UnsupportedTypeError) as excinfo:
+        function_typing.sdk_type_from_python_type(unsupported_type)
+    assert "list[str]" in str(excinfo.value)
+    assert "bool, bytes, float, int, str" in str(excinfo.value)