diff --git a/master.cfg b/master.cfg
index 99c72c6..3ec1460 100644
--- a/master.cfg
+++ b/master.cfg
@@ -229,7 +229,9 @@ subsequent commits are made after X, by different people."""
 
     # This file will be cleaned the next time we run
     # MessageGDBTesters, iff the build breakage has been fixed.
-    open (lockfile, 'w').close ()
+    bf = open (lockfile, 'w')
+    bf.write ("Commit that caused the breakage: %s\n" % change.revision)
+    bf.close ()
 
     rev = change.revision
     to = change.who.encode ('ascii', 'ignore').decode ('ascii')