diff --git a/contrib/prepare-commit-msg b/contrib/prepare-commit-msg
index 820dacc7e42..fd59bfbcf88 100755
--- a/contrib/prepare-commit-msg
+++ b/contrib/prepare-commit-msg
@@ -54,4 +54,9 @@ else
     exit 0
 fi
 
+# Save diff to a file if requested.
+if ! [ -z "$GCC_GIT_DIFF_FILE" ]; then
+  git $cmd > "$GCC_GIT_DIFF_FILE";
+fi
+
 git $cmd | git gcc-mklog -c "$COMMIT_MSG_FILE"