diff --git a/tools/python/xen/xm/main.py b/tools/python/xen/xm/main.py
index e27393c505..32315860c4 100644
--- a/tools/python/xen/xm/main.py
+++ b/tools/python/xen/xm/main.py
@@ -417,10 +417,11 @@ server = None
 def cmdHelp(cmd):
     """Print help for a specific subcommand."""
     
-    for fc in SUBCOMMAND_HELP.keys():
-        if fc[:len(cmd)] == cmd:
-            cmd = fc
-            break
+    if not SUBCOMMAND_HELP.has_key(cmd):
+        for fc in SUBCOMMAND_HELP.keys():
+            if fc[:len(cmd)] == cmd:
+                cmd = fc
+                break
     
     try:
         args, desc = SUBCOMMAND_HELP[cmd]