--- a/mercurial/commands.py	Sat Mar 08 18:41:56 2014 +0900
+++ b/mercurial/commands.py	Sat Mar 08 18:52:16 2014 +0900
@@ -416,7 +416,8 @@
 
     See :hg:`help dates` for a list of formats valid for -d/--date.
 
-    Returns 0 on success, 1 if there are unresolved files.
+    Returns 0 on success, 1 if nothing to backout or there are unresolved
+    files.
     '''
     if rev and node:
         raise util.Abort(_("please specify just one revision"))
@@ -495,6 +496,9 @@
             return repo.commit(message, opts.get('user'), opts.get('date'),
                                match, editor=e)
         newnode = cmdutil.commit(ui, repo, commitfunc, [], opts)
+        if not newnode:
+            ui.status(_("nothing changed\n"))
+            return 1
         cmdutil.commitstatus(repo, newnode, branch, bheads)
 
         def nice(node):

--- a/tests/test-backout.t	Sat Mar 08 18:41:56 2014 +0900
+++ b/tests/test-backout.t	Sat Mar 08 18:52:16 2014 +0900
@@ -409,6 +409,22 @@
 
   $ cd ..
 
+backout of empty changeset (issue4190)
+
+  $ hg init emptycommit
+  $ cd emptycommit
+
+  $ touch file1
+  $ hg ci -Aqm file1
+  $ hg branch -q branch1
+  $ hg ci -qm branch1
+  $ hg backout -v 1
+  resolving manifests
+  nothing changed
+  [1]
+
+  $ cd ..
+
 
 Test usage of `hg resolve` in case of conflict
 (issue4163)