diff --git a/mercurial/localrepo.py b/mercurial/localrepo.py
--- a/mercurial/localrepo.py
+++ b/mercurial/localrepo.py
@@ -1377,7 +1377,7 @@ class localrepository(object):
             wctx = self[None]
             merge = len(wctx.parents()) > 1
 
-            if not force and merge and not match.always():
+            if not force and merge and match.ispartial():
                 raise util.Abort(_('cannot partially commit a merge '
                                    '(do not specify files or patterns)'))
 
diff --git a/mercurial/match.py b/mercurial/match.py
--- a/mercurial/match.py
+++ b/mercurial/match.py
@@ -186,6 +186,14 @@ class match(object):
         - optimization might be possible and necessary.'''
         return self._always
 
+    def ispartial(self):
+        '''True if the matcher won't always match.
+
+        Although it's just the inverse of _always in this implementation,
+        an extenion such as narrowhg might make it return something
+        slightly different.'''
+        return not self._always
+
     def isexact(self):
         return self.matchfn == self.exact