diff --git a/checkpatch.sh b/checkpatch.sh
index 3ce56b7a..5393799d 100755
--- a/checkpatch.sh
+++ b/checkpatch.sh
@@ -165,7 +165,7 @@ function clang_style()
     echo "{ $(sed -e 's/#.*//' -e '/---/d' -e '/\.\.\./d' "$c" | tr $'\n' ,) }"
 }
 function clang_format() { clang-format -style="$(clang_style)" "$@"; }
-function clang_format_diff() { clang-format-diff -style="$(clang_style)" "$@"; }
+function clang_format_diff() { cat "$@" | clang-format-diff -p1 -style="$(clang_style)"; }
 # for non-bare repo will work
 function clang_format_git()
 { git format-patch --stdout "$@" -1 | clang_format_diff; }