diff --git a/Tests/test_file_tiff_metadata.py b/Tests/test_file_tiff_metadata.py
index d7a18c72504..8b816aa4fb5 100644
--- a/Tests/test_file_tiff_metadata.py
+++ b/Tests/test_file_tiff_metadata.py
@@ -224,14 +224,17 @@ def test_writing_other_types_to_bytes(value: int | IFDRational, tmp_path: Path)
         assert reloaded.tag_v2[700] == b"\x01"
 
 
-def test_writing_other_types_to_undefined(tmp_path: Path) -> None:
+@pytest.mark.parametrize("value", (1, IFDRational(1)))
+def test_writing_other_types_to_undefined(
+    value: int | IFDRational, tmp_path: Path
+) -> None:
     im = hopper()
     info = TiffImagePlugin.ImageFileDirectory_v2()
 
     tag = TiffTags.TAGS_V2[33723]
     assert tag.type == TiffTags.UNDEFINED
 
-    info[33723] = 1
+    info[33723] = value
 
     out = str(tmp_path / "temp.tiff")
     im.save(out, tiffinfo=info)
diff --git a/src/PIL/TiffImagePlugin.py b/src/PIL/TiffImagePlugin.py
index 3ba4de9d12e..b59139f5858 100644
--- a/src/PIL/TiffImagePlugin.py
+++ b/src/PIL/TiffImagePlugin.py
@@ -790,6 +790,8 @@ def load_undefined(self, data, legacy_api=True):
 
     @_register_writer(7)
     def write_undefined(self, value):
+        if isinstance(value, IFDRational):
+            value = int(value)
         if isinstance(value, int):
             value = str(value).encode("ascii", "replace")
         return value