diff --git a/hgext/hooklib/reject_new_heads.py b/hgext/hooklib/reject_new_heads.py
--- a/hgext/hooklib/reject_new_heads.py
+++ b/hgext/hooklib/reject_new_heads.py
@@ -4,8 +4,8 @@
 # GNU General Public License version 2 or any later version.
 
 """reject_new_heads is a hook to check that branches touched by new changesets
-have at most one open head. It can be used to enforce policies for
-merge-before-push or rebase-before-push. It does not handle pre-existing
+or phase transitions have at most one open head. It can be used to enforce policies
+for merge-before-push or rebase-before-push. It does not handle pre-existing
 hydras.
 
 Usage:
@@ -30,9 +30,14 @@
         )
     ctx = repo.unfiltered()[node]
     branches = set()
-    for rev in repo.changelog.revs(start=ctx.rev()):
-        rev = repo[rev]
-        branches.add(rev.branch())
+    if ctx.rev():
+        for rev in repo.changelog.revs(start=ctx.rev()):
+            rev = repo[rev]
+            branches.add(rev.branch())
+    for revs, (old, new) in kwargs.get('changes', {b'phases': []})[b'phases']:
+        for rev in revs:
+            branches.add(repo.unfiltered()[rev].branch())
+
     for branch in branches:
         if len(repo.revs("head() and not closed() and branch(%s)", branch)) > 1:
             raise error.Abort(
diff --git a/tests/test-hooklib-reject_new_heads.t b/tests/test-hooklib-reject_new_heads.t
--- a/tests/test-hooklib-reject_new_heads.t
+++ b/tests/test-hooklib-reject_new_heads.t
@@ -5,6 +5,7 @@
   > [phases]
   > publish = False
   > EOF
+
   $ hg init a
   $ hg --cwd a debugbuilddag '.:parent.*parent'
   $ hg --cwd a log -G
@@ -26,6 +27,7 @@
      date:        Thu Jan 01 00:00:00 1970 +0000
      summary:     r0
   
+
   $ hg init b
   $ cat <<EOF >> b/.hg/hgrc
   > [hooks]
@@ -43,11 +45,61 @@
   rollback completed
   abort: Changes on branch 'default' resulted in multiple heads
   [255]
-  $ hg --cwd b pull ../a -r 1ea73414a91b
+  $ hg --cwd b pull ../a -r 66f7d451a68b
   pulling from ../a
   adding changesets
   adding manifests
   adding file changes
-  added 1 changesets with 0 changes to 0 files
-  new changesets 1ea73414a91b (1 drafts)
+  added 2 changesets with 0 changes to 0 files
+  new changesets 1ea73414a91b:66f7d451a68b (2 drafts)
   (run 'hg update' to get a working copy)
+
+  $ hg --cwd b phase --public 66f7d451a68b
+  $ hg --cwd b --config hooks.pretxnclose.reject_new_heads= pull ../a
+  pulling from ../a
+  searching for changes
+  adding changesets
+  adding manifests
+  adding file changes
+  added 1 changesets with 0 changes to 0 files (+1 heads)
+  new changesets fa942426a6fd (1 drafts)
+  (run 'hg heads' to see heads, 'hg merge' to merge)
+
+Test that pushing a draft change to a publishing server having the same
+change already still triggers the check on the phase transition. The
+changeset should remain as draft.
+
+  $ cat <<EOF >> b/.hg/hgrc
+  > [serve]
+  > view = immutable
+  > 
+  > [phases]
+  > publish = True
+  > EOF
+
+  $ cat > web.conf << EOF
+  > [paths]
+  > / = *
+  > 
+  > [web]
+  > push_ssl = false
+  > allow_push = *
+  > EOF
+
+  $ hg --cwd b serve --web-conf ../web.conf -p $HGPORT -d --pid-file ../hg.pid
+  $ cat hg.pid >> $DAEMON_PIDS
+
+  $ hg --cwd a push -f http://localhost:$HGPORT
+  pushing to http://localhost:$HGPORT/
+  searching for changes
+  no changes found
+  remote: error: pretxnclose.reject_new_heads hook failed: Changes on branch 'default' resulted in multiple heads
+  remote: Changes on branch 'default' resulted in multiple heads
+  abort: push failed on remote
+  [255]
+  $ hg phase --cwd b fa942426a6fd
+  2: draft
+
+Cleanup.
+
+  $ killdaemons.py