--- a/mercurial/filemerge.py	Mon Oct 02 04:46:17 2017 +0530
+++ b/mercurial/filemerge.py	Mon Oct 02 04:48:06 2017 +0530
@@ -515,7 +515,7 @@
                            (tool, fcd.path()))
         repo.ui.debug('launching merge tool: %s\n' % cmd)
         r = ui.system(cmd, cwd=repo.root, environ=env, blockedtag='mergetool')
-        repo.ui.debug('merge tool returned: %s\n' % r)
+        repo.ui.debug('merge tool returned: %d\n' % r)
         return True, r, False
     finally:
         util.unlink(b)