diff --git a/bob/extension/utils.py b/bob/extension/utils.py
index d83b62ec598d68f9064755753f974f678bc28757..277092eb422337a55ea44c6e0b003a5552cb17b0 100644
--- a/bob/extension/utils.py
+++ b/bob/extension/utils.py
@@ -233,7 +233,7 @@ def link_documentation(
                     )
                 except pkg_resources.DistributionNotFound:
                     version = "stable"  # package is not a runtime dep, only referenced
-                url = s % {"name":package_name, "version":version}
+                url = s % {"name": package_name, "version": version}
 
             try:
                 # otherwise, urlopen will fail