mercurial/commands.py

--- a/mercurial/commands.py	Fri Apr 18 18:26:42 2014 -0700
+++ b/mercurial/commands.py	Fri Apr 18 19:08:32 2014 -0700
@@ -4927,6 +4927,10 @@
                            'use --all to remerge all files'))
 
     ms = mergemod.mergestate(repo)
+
+    if not ms.active():
+        raise util.Abort(_('resolve command not applicable when not merging'))
+
     m = scmutil.match(repo[None], pats, opts)
     ret = 0