diff --git a/mercurial/commands.py b/mercurial/commands.py
--- a/mercurial/commands.py
+++ b/mercurial/commands.py
@@ -4168,17 +4168,43 @@ def merge(ui, repo, node=None, **opts):
     if not node:
         node = opts.get('rev')
 
-    if not node:
+    if node:
+        node = scmutil.revsingle(repo, node).node()
+
+    if not node and repo._bookmarkcurrent:
+        bmheads = repo.bookmarkheads(repo._bookmarkcurrent)
+        curhead = repo[repo._bookmarkcurrent]
+        if len(bmheads) == 2:
+            if curhead == bmheads[0]:
+                node = bmheads[1]
+            else:
+                node = bmheads[0]
+        elif len(bmheads) > 2:
+            raise util.Abort(_("multiple matching bookmarks to merge - "
+                "please merge with an explicit rev or bookmark"),
+                hint=_("run 'hg heads' to see all heads"))
+        elif len(bmheads) <= 1:
+            raise util.Abort(_("no matching bookmark to merge - "
+                "please merge with an explicit rev or bookmark"),
+                hint=_("run 'hg heads' to see all heads"))
+
+    if not node and not repo._bookmarkcurrent:
         branch = repo[None].branch()
         bheads = repo.branchheads(branch)
-        if len(bheads) > 2:
+        nbhs = [bh for bh in bheads if not repo[bh].bookmarks()]
+
+        if len(nbhs) > 2:
             raise util.Abort(_("branch '%s' has %d heads - "
                                "please merge with an explicit rev")
                              % (branch, len(bheads)),
                              hint=_("run 'hg heads .' to see heads"))
 
         parent = repo.dirstate.p1()
-        if len(bheads) == 1:
+        if len(nbhs) == 1:
+            if len(bheads) > 1:
+                raise util.Abort(_("heads are bookmarked - "
+                                   "please merge with an explicit rev"),
+                                 hint=_("run 'hg heads' to see all heads"))
             if len(repo.heads()) > 1:
                 raise util.Abort(_("branch '%s' has one head - "
                                    "please merge with an explicit rev")
@@ -4193,9 +4219,10 @@ def merge(ui, repo, node=None, **opts):
             raise util.Abort(_('working directory not at a head revision'),
                              hint=_("use 'hg update' or merge with an "
                                     "explicit revision"))
-        node = parent == bheads[0] and bheads[-1] or bheads[0]
-    else:
-        node = scmutil.revsingle(repo, node).node()
+        if parent == nbhs[0]:
+            node = nbhs[-1]
+        else:
+            node = nbhs[0]
 
     if opts.get('preview'):
         # find nodes that are ancestors of p2 but not of p1
diff --git a/tests/test-bookmarks-merge.t b/tests/test-bookmarks-merge.t
--- a/tests/test-bookmarks-merge.t
+++ b/tests/test-bookmarks-merge.t
@@ -29,3 +29,65 @@
   $ hg bookmarks
      b                         1:d2ae7f538514
    * c                         3:b8f96cf4688b
+
+  $ hg up -C 3
+  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ echo d > d
+  $ hg add d
+  $ hg commit -m'd'
+
+  $ hg up -C 3
+  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  $ echo e > e
+  $ hg add e
+  $ hg commit -m'e'
+  created new head
+  $ hg up -C 5
+  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  $ hg bookmark e
+  $ hg bookmarks
+     b                         1:d2ae7f538514
+     c                         3:b8f96cf4688b
+   * e                         5:26bee9c5bcf3
+
+# the picked side is bookmarked
+
+  $ hg up -C 4
+  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  $ hg merge
+  abort: heads are bookmarked - please merge with an explicit rev
+  (run 'hg heads' to see all heads)
+  [255]
+
+# our revision is bookmarked
+
+  $ hg up -C e
+  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  $ hg merge
+  abort: no matching bookmark to merge - please merge with an explicit rev or bookmark
+  (run 'hg heads' to see all heads)
+  [255]
+
+# merge bookmark heads
+
+  $ hg up -C 4
+  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  $ echo f > f
+  $ hg commit -Am "f"
+  adding f
+  $ hg up -C e
+  1 files updated, 0 files merged, 2 files removed, 0 files unresolved
+  $ hg bookmarks -r 4 "e@diverged"
+  $ hg bookmarks
+     b                         1:d2ae7f538514
+     c                         3:b8f96cf4688b
+   * e                         5:26bee9c5bcf3
+     e@diverged                4:a0546fcfe0fb
+  $ hg merge
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  (branch merge, don't forget to commit)
+  $ hg commit -m'merge'
+  $ hg bookmarks
+     b                         1:d2ae7f538514
+     c                         3:b8f96cf4688b
+   * e                         7:ca784329f0ba
diff --git a/tests/test-convert-hg-source.t b/tests/test-convert-hg-source.t
--- a/tests/test-convert-hg-source.t
+++ b/tests/test-convert-hg-source.t
@@ -19,7 +19,7 @@
   $ hg ci -m 'make bar and baz copies of foo' -d '2 0'
   created new head
   $ hg bookmark premerge1
-  $ hg merge
+  $ hg merge -r 1
   merging baz and foo to baz
   1 files updated, 1 files merged, 0 files removed, 0 files unresolved
   (branch merge, don't forget to commit)