diff --git a/mercurial/commandserver.py b/mercurial/commandserver.py
--- a/mercurial/commandserver.py
+++ b/mercurial/commandserver.py
@@ -449,6 +449,8 @@ class unixforkingservice(object):
     def init(self):
         self._sock = socket.socket(socket.AF_UNIX)
         self._servicehandler.bindsocket(self._sock, self.address)
+        if util.safehasattr(util, 'unblocksignal'):
+            util.unblocksignal(signal.SIGCHLD)
         o = signal.signal(signal.SIGCHLD, self._sigchldhandler)
         self._oldsigchldhandler = o
         self._socketunlinked = False