--- a/tests/run-tests.py	Sun Dec 16 15:47:08 2018 -0500
+++ b/tests/run-tests.py	Sun Dec 16 17:36:51 2018 -0500
@@ -2640,6 +2640,9 @@
             self._tmpbindir = self._bindir
             self._pythondir = os.path.join(self._installdir, b"lib", b"python")
 
+        if os.name == 'nt' and not self._hgcommand.endswith(b'.exe'):
+            self._hgcommand += b'.exe'
+
         # set CHGHG, then replace "hg" command by "chg"
         chgbindir = self._bindir
         if self.options.chg or self.options.with_chg: