diff -r 6390c377a9e6 -r 9a0af739cf55 mercurial/commands.py
--- a/mercurial/commands.py	Tue Aug 09 09:36:34 2005 -0800
+++ b/mercurial/commands.py	Fri Aug 12 09:57:56 2005 -0800
@@ -634,9 +634,11 @@
         raise Abort("too many revisions to diff")
 
     files = []
-    roots, match, results = makewalk(repo, pats, opts)
-    for src, abs, rel in results:
-        files.append(abs)
+    match = util.always
+    if pats:
+        roots, match, results = makewalk(repo, pats, opts)
+        for src, abs, rel in results:
+            files.append(abs)
     dodiff(sys.stdout, ui, repo, files, *revs, **{'match': match})
 
 def doexport(ui, repo, changeset, seqno, total, revwidth, opts):