diff --git a/lib/locale.t b/lib/locale.t
index 80a18b14c760..4fd26db2019c 100644
--- a/lib/locale.t
+++ b/lib/locale.t
@@ -107,7 +107,7 @@ my $dumper = Dumpvalue->new(
 
 sub debug {
   return unless $debug;
-  my($mess) = join "", '# ', @_;
+  my($mess) = join "", '# ', __FILE__, ": ", @_;
   chomp $mess;
   print STDERR $dumper->stringify($mess,1), "\n";
 }