diff --git a/mercurial/cmdutil.py b/mercurial/cmdutil.py
--- a/mercurial/cmdutil.py
+++ b/mercurial/cmdutil.py
@@ -1899,7 +1899,7 @@
     # wanted: a cache of filenames that were changed (ctx.files()) and that
     # match the file filtering conditions.
 
-    if match.always():
+    if match.always() or allfiles:
         # No files, no patterns.  Display all revs.
         wanted = revs
     elif not slowpath:
diff --git a/tests/test-grep.t b/tests/test-grep.t
--- a/tests/test-grep.t
+++ b/tests/test-grep.t
@@ -500,4 +500,8 @@
   $ hg grep -r "0:2" "unmod" --all-files
   um:0:unmod
   um:1:unmod
+  $ hg grep -r "0:2" "unmod" --all-files um
+  um:0:unmod
+  um:1:unmod
   $ cd ..
+