--- a/mercurial/cmdutil.py	Thu Dec 01 20:42:24 2011 +0100
+++ b/mercurial/cmdutil.py	Thu Dec 01 15:51:36 2011 -0600
@@ -23,7 +23,14 @@
     """
     choice = {}
     debugchoice = {}
-    for e in table.keys():
+
+    if cmd in table:
+        # short-circuit exact matches, "log" alias beats "^log|history"
+        keys = [cmd]
+    else:
+        keys = table.keys()
+
+    for e in keys:
         aliases = parsealiases(e)
         found = None
         if cmd in aliases: