diff --git a/mercurial/fileset.py b/mercurial/fileset.py
--- a/mercurial/fileset.py
+++ b/mercurial/fileset.py
@@ -485,7 +485,7 @@ def getfileset(ctx, expr):
             subset.extend(c)
     else:
         status = None
-        subset = ctx.walk(ctx.match([]))
+        subset = list(ctx.walk(ctx.match([])))
 
     return getset(matchctx(ctx, subset, status), tree)
 
diff --git a/tests/test-cat.t b/tests/test-cat.t
--- a/tests/test-cat.t
+++ b/tests/test-cat.t
@@ -21,3 +21,14 @@
   [1]
   $ hg cat -r 1 b
   1
+
+Test fileset
+
+  $ echo 3 > c
+  $ hg ci -Am addmore c
+  $ hg cat 'set:not(b) or a'
+  3
+  $ hg cat 'set:c or b'
+  1
+  3
+
diff --git a/tests/test-fileset.t b/tests/test-fileset.t
--- a/tests/test-fileset.t
+++ b/tests/test-fileset.t
@@ -222,4 +222,7 @@ Test with a revision
   sub
   $ fileset -r4 'subrepo("sub")'
   sub
+  $ fileset -r4 'b2 or c1'
+  b2
+  c1