diff -r 72d88a975655 -r 246b61bfdc2f mercurial/utils/procutil.py
--- a/mercurial/utils/procutil.py	Fri Nov 23 22:18:56 2018 -0500
+++ b/mercurial/utils/procutil.py	Fri Nov 23 22:27:57 2018 -0500
@@ -241,7 +241,7 @@
                 _sethgexecutable(encoding.environ['EXECUTABLEPATH'])
             else:
                 _sethgexecutable(pycompat.sysexecutable)
-        elif (os.path.basename(
+        elif (not pycompat.iswindows and os.path.basename(
             pycompat.fsencode(getattr(mainmod, '__file__', ''))) == 'hg'):
             _sethgexecutable(pycompat.fsencode(mainmod.__file__))
         else: