diff --git a/mercurial/commands.py b/mercurial/commands.py
--- a/mercurial/commands.py
+++ b/mercurial/commands.py
@@ -3428,8 +3428,11 @@
                 m = regexp.search(self.line, p)
                 if not m:
                     break
-                yield m.span()
-                p = m.end()
+                if m.end() == p:
+                    p += 1
+                else:
+                    yield m.span()
+                    p = m.end()
 
     matches = {}
     copies = {}
diff --git a/tests/test-grep.t b/tests/test-grep.t
--- a/tests/test-grep.t
+++ b/tests/test-grep.t
@@ -660,7 +660,7 @@
   $ echo 'added, missing' > added-missing; hg add added-missing; rm added-missing
   $ echo 'untracked' > untracked
   $ hg rm old
-  $ hg grep '[^Z]'
+  $ hg grep ''
   added:added
   new:something else
   new:modified