diff --git a/hgext/patchbomb.py b/hgext/patchbomb.py
--- a/hgext/patchbomb.py
+++ b/hgext/patchbomb.py
@@ -451,7 +451,10 @@ def patchbomb(ui, repo, *revs, **opts):
             ui.status(_('Writing '), subj, ' ...\n')
             fp = open(opts.get('mbox'), 'In-Reply-To' in m and 'ab+' or 'wb+')
             generator = email.Generator.Generator(fp, mangle_from_=True)
-            date = time.ctime(start_time[0])
+            # Should be time.asctime(), but Windows prints 2-characters day
+            # of month instead of one. Make them print the same thing.
+            date = time.strftime('%a %b %d %H:%M:%S %Y',
+                                 time.localtime(start_time[0]))
             fp.write('From %s %s\n' % (sender_addr, date))
             generator.flatten(m, 0)
             fp.write('\n\n')
diff --git a/tests/test-patchbomb.out b/tests/test-patchbomb.out
--- a/tests/test-patchbomb.out
+++ b/tests/test-patchbomb.out
@@ -163,7 +163,7 @@ This patch series consists of 1 patches.
 
 
 Writing [PATCH] charset=utf-8; content-transfer-encoding: base64 ...
-From quux Thu Jan  1 00:04:01 1970
+From quux Thu Jan 01 00:04:01 1970
 Content-Type: text/plain; charset="utf-8"
 MIME-Version: 1.0
 Content-Transfer-Encoding: base64
@@ -198,7 +198,7 @@ This patch series consists of 1 patches.
 
 
 Writing [PATCH] charset=utf-8; content-transfer-encoding: quoted-printable ...
-From quux Thu Jan  1 00:04:01 1970
+From quux Thu Jan 01 00:04:01 1970
 Content-Type: text/plain; charset="us-ascii"
 MIME-Version: 1.0
 Content-Transfer-Encoding: quoted-printable
@@ -249,7 +249,7 @@ This patch series consists of 1 patches.
 
 Writing [PATCH] charset=us-ascii; content-transfer-encoding: 8bit ...
 % md5sum of 8-bit output
-0920ef519c29b6a1742047ad9f203fc5  mboxfix
+9ea043d8fc43a71045114508baed144b  mboxfix
 % test diffstat for single patch
 This patch series consists of 1 patches.
 
@@ -1474,7 +1474,7 @@ This patch series consists of 1 patches.
 
 
 Writing [PATCH] test ...
-From quux Tue Jan  1 00:01:01 1980
+From quux Tue Jan 01 00:01:01 1980
 Content-Type: text/plain; charset="us-ascii"
 MIME-Version: 1.0
 Content-Transfer-Encoding: 7bit