diff --git a/.gitignore b/.gitignore
index 164b1c6..28add6d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,4 @@
 /build/
 /dist/
-*.egg_info
 /.idea/
+/tiffwrite.egg-info/
diff --git a/setup.py b/setup.py
index 8d107f7..53fa835 100644
--- a/setup.py
+++ b/setup.py
@@ -5,7 +5,7 @@ with open('README.md', 'r') as fh:
 
 setuptools.setup(
     name='tiffwrite',
-    version='2022.5.0',
+    version='2022.5.1',
     author='Wim Pomp @ Lenstra lab NKI',
     author_email='w.pomp@nki.nl',
     description='Parallel tiff writer compatible with ImageJ.',
diff --git a/tiffwrite/__init__.py b/tiffwrite/__init__.py
index 4bbb009..1de8f87 100755
--- a/tiffwrite/__init__.py
+++ b/tiffwrite/__init__.py
@@ -104,8 +104,8 @@ class Tag:
 
     @staticmethod
     def fraction(numerator=0, denominator=None):
-        return Fraction(numerator, denominator).limit_denominator(2 ** (31 if numerator < 0 or denominator < 0
-                                                                        else 32) - 1)
+        return Fraction(numerator, denominator).limit_denominator(2 ** (31 if numerator < 0 or
+                                                             (denominator is not None and denominator < 0) else 32) - 1)
 
     def __init__(self, ttype, value=None, offset=None):
         if value is None: