diff -r b520c8f98e1e -r 8652ab4046e4 mercurial/util.py
--- a/mercurial/util.py	Mon Dec 18 21:15:53 2017 +0900
+++ b/mercurial/util.py	Wed Dec 20 02:13:35 2017 -0800
@@ -163,6 +163,10 @@
     setprocname = osutil.setprocname
 except AttributeError:
     pass
+try:
+    unblocksignal = osutil.unblocksignal
+except AttributeError:
+    pass
 
 # Python compatibility