diff --git a/tools/wrap-commit-msg.py b/tools/wrap-commit-msg.py
index b53926ae1..d5b4b046b 100755
--- a/tools/wrap-commit-msg.py
+++ b/tools/wrap-commit-msg.py
@@ -59,6 +59,7 @@ def main(fileobj):
     if fileobj == sys.stdin:
         fileobj = sys.stdout
     else:
+        fileobj.seek(0)
         fileobj.truncate(0)
     fileobj.write(output)