diff -r 3a333a582d7b -r 60eb35b0c11c hgext/remotefilelog/shallowrepo.py
--- a/hgext/remotefilelog/shallowrepo.py	Thu Sep 27 13:03:19 2018 -0400
+++ b/hgext/remotefilelog/shallowrepo.py	Wed Oct 03 13:54:45 2018 -0400
@@ -199,9 +199,7 @@
                 cmd.append('--repack')
             if revs:
                 cmd += ['-r', revs]
-            cmd = ' '.join(map(procutil.shellquote, cmd))
-
-            extutil.runshellcommand(cmd, encoding.environ)
+            extutil.runbgcommand(cmd, encoding.environ)
 
         def prefetch(self, revs, base=None, pats=None, opts=None):
             """Prefetches all the necessary file revisions for the given revs