diff --git a/hgext/patchbomb.py b/hgext/patchbomb.py
--- a/hgext/patchbomb.py
+++ b/hgext/patchbomb.py
@@ -384,7 +384,7 @@ def patchbomb(ui, repo, *revs, **opts):
         prefix = '[PATCH %0*d of %d%s]' % (tlen, 0, len(patches), flag)
 
         subj = (opts.get('subject') or
-                prompt(ui, 'Subject: ', rest=prefix, default=''))
+                prompt(ui, '(optional) Subject: ', rest=prefix, default=''))
         if not subj:
             return None         # skip intro if the user doesn't bother
 
diff --git a/tests/test-patchbomb.t b/tests/test-patchbomb.t
--- a/tests/test-patchbomb.t
+++ b/tests/test-patchbomb.t
@@ -1572,7 +1572,7 @@ no intro message in non-interactive mode
   >  -r 0:1
   This patch series consists of 2 patches.
   
-  Subject: [PATCH 0 of 2] 
+  (optional) Subject: [PATCH 0 of 2] 
   
   Displaying [PATCH 1 of 2] a ...
   Content-Type: text/plain; charset="us-ascii"