diff --git a/util/style/repo.py b/util/style/repo.py
index 1943e48b6..adcbdc95f 100644
--- a/util/style/repo.py
+++ b/util/style/repo.py
@@ -185,7 +185,7 @@ class GitRepo(AbstractRepo):
         if cached:
             cmd.append("--cached")
         if filter:
-            cmd += [ "--diff-filter", filter ]
+            cmd += [ "--diff-filter=%s" % filter ]
         cmd += [ self.head_revision(), "--" ] + files
         status = subprocess.check_output(cmd).rstrip("\n")