diff -r a7f8c657a3f0 -r b746a22349f9 mercurial/ui.py
--- a/mercurial/ui.py	Thu Mar 05 11:02:07 2020 -0500
+++ b/mercurial/ui.py	Thu Mar 19 16:06:24 2020 +0100
@@ -1868,7 +1868,7 @@
             rc = self._runsystem(cmd, environ=environ, cwd=cwd, out=out)
         if rc and onerr:
             errmsg = b'%s %s' % (
-                os.path.basename(cmd.split(None, 1)[0]),
+                procutil.shellsplit(cmd)[0],
                 procutil.explainexit(rc),
             )
             if errprefix: