--- a/tests/run-tests.py	Mon Nov 08 10:56:47 2010 +0100
+++ b/tests/run-tests.py	Tue Nov 16 10:33:19 2010 +0900
@@ -504,7 +504,8 @@
         vlog("# Running", cmd)
         exitcode, output = run(cmd, options, replacements)
         # do not merge output if skipped, return hghave message instead
-        if exitcode == SKIPPED_STATUS:
+        # similarly, with --debug, output is None
+        if exitcode == SKIPPED_STATUS or output is None:
             return exitcode, output
     finally:
         os.remove(name)