diff --git a/mercurial/merge.py b/mercurial/merge.py
--- a/mercurial/merge.py
+++ b/mercurial/merge.py
@@ -1341,8 +1341,12 @@ def update(repo, node, branchmerge, forc
         fp1, fp2, xp1, xp2 = p1.node(), p2.node(), str(p1), str(p2)
 
         ### check phase
-        if not overwrite and len(pl) > 1:
-            raise error.Abort(_("outstanding uncommitted merge"))
+        if not overwrite:
+            if len(pl) > 1:
+                raise error.Abort(_("outstanding uncommitted merge"))
+            ms = mergestate.read(repo)
+            if list(ms.unresolved()):
+                raise error.Abort(_("outstanding merge conflicts"))
         if branchmerge:
             if pas == [p2]:
                 raise error.Abort(_("merging with a working directory ancestor"
diff --git a/tests/test-merge-local.t b/tests/test-merge-local.t
--- a/tests/test-merge-local.t
+++ b/tests/test-merge-local.t
@@ -59,6 +59,9 @@ Local merge with bad merge tool:
   use 'hg resolve' to retry unresolved file merges
   [1]
 
+  $ hg resolve -m
+  (no more unresolved files)
+
   $ hg co 0
   merging zzz1_merge_ok
   merging zzz2_merge_bad
@@ -83,6 +86,9 @@ Local merge with bad merge tool:
 
 Local merge with conflicts:
 
+  $ hg resolve -m
+  (no more unresolved files)
+
   $ hg co
   merging zzz1_merge_ok
   merging zzz2_merge_bad
@@ -91,6 +97,9 @@ Local merge with conflicts:
   use 'hg resolve' to retry unresolved file merges
   [1]
 
+  $ hg resolve -m
+  (no more unresolved files)
+
   $ hg co 0 --config 'ui.origbackuppath=.hg/origbackups'
   merging zzz1_merge_ok
   merging zzz2_merge_bad
@@ -124,6 +133,9 @@ Local merge without conflicts:
 
   $ hg revert zzz2_merge_bad
 
+  $ hg resolve -m
+  (no more unresolved files)
+
   $ hg co
   merging zzz1_merge_ok
   4 files updated, 1 files merged, 2 files removed, 0 files unresolved
diff --git a/tests/test-resolve.t b/tests/test-resolve.t
--- a/tests/test-resolve.t
+++ b/tests/test-resolve.t
@@ -154,6 +154,26 @@ resolve -m should abort when no merge in
   abort: resolve command not applicable when not merging
   [255]
 
+can not update or merge when there are unresolved conflicts
+
+  $ hg up -qC 0
+  $ echo quux >> file1
+  $ hg up 1
+  merging file1
+  warning: conflicts while merging file1! (edit, then use 'hg resolve --mark')
+  1 files updated, 0 files merged, 0 files removed, 1 files unresolved
+  use 'hg resolve' to retry unresolved file merges
+  [1]
+  $ hg up 0
+  abort: outstanding merge conflicts
+  [255]
+  $ hg merge 2
+  abort: outstanding merge conflicts
+  [255]
+  $ hg merge --force 2
+  abort: outstanding merge conflicts
+  [255]
+
 set up conflict-free merge
 
   $ hg up -qC 3