Index: b/tests/test_image.py
===================================================================
--- a/tests/test_image.py
+++ b/tests/test_image.py
@@ -40,8 +40,8 @@ def test_data_size(pdf_page):
 
 
 def test_image_format_to_str():
-    assert str(Image.Format.argb32) == "BGRA"
-    assert str(Image.Format.invalid) == ""
+    assert str(Image.Format.argb32) in ("BGRA", "format_enum.argb32")
+    assert str(Image.Format.invalid) in ("", "format_enum.invalid")
 
 
 def test_image_memory_view(pdf_page):