diff --git a/hgext/patchbomb.py b/hgext/patchbomb.py
--- a/hgext/patchbomb.py
+++ b/hgext/patchbomb.py
@@ -496,8 +496,6 @@ def patchbomb(ui, repo, *revs, **opts):
         if not parent.endswith('>'):
             parent += '>'
 
-    first = True
-
     sender_addr = email.Utils.parseaddr(sender)[1]
     sender = mail.addressencode(ui, sender, _charsets, opts.get('test'))
     sendmail = None
@@ -509,9 +507,8 @@ def patchbomb(ui, repo, *revs, **opts):
         if parent:
             m['In-Reply-To'] = parent
             m['References'] = parent
-        if first:
+        if not parent or 'X-Mercurial-Node' not in m:
             parent = m['Message-Id']
-            first = False
 
         m['User-Agent'] = 'Mercurial-patchbomb/%s' % util.version()
         m['Date'] = email.Utils.formatdate(start_time[0], localtime=True)
diff --git a/tests/test-patchbomb.t b/tests/test-patchbomb.t
--- a/tests/test-patchbomb.t
+++ b/tests/test-patchbomb.t
@@ -1663,8 +1663,8 @@ no intro message in non-interactive mode
   Subject: [PATCH 2 of 2] b
   X-Mercurial-Node: 97d72e5f12c7e84f85064aa72e5a297142c36ed9
   Message-Id: <97d72e5f12c7e84f8506.61@*> (glob)
-  In-Reply-To: <8580ff50825a50c8f716.60@*> (glob)
-  References: <8580ff50825a50c8f716.60@*> (glob)
+  In-Reply-To: <baz>
+  References: <baz>
   User-Agent: Mercurial-patchbomb/* (glob)
   Date: Thu, 01 Jan 1970 00:01:01 +0000
   From: quux