--- a/hgext3rd/evolve/obscache.py	Tue Jul 25 05:14:37 2017 +0200
+++ b/hgext3rd/evolve/obscache.py	Tue Jul 25 05:51:44 2017 +0200
@@ -22,7 +22,6 @@
     pycompat,
     node,
     util,
-    vfs as vfsmod,
 )
 
 from mercurial.i18n import _
@@ -43,6 +42,12 @@
 else:
     timer = time.time
 
+# hg < 4.2 compat
+try:
+    from mercurial import vfs as vfsmod
+    vfsmod.vfs
+except ImportError:
+    from mercurial import scmutil as vfsmod
 
 try:
     obsstorefilecache = localrepo.localrepository.obsstore