diff --git a/mercurial/pycompat.py b/mercurial/pycompat.py
--- a/mercurial/pycompat.py
+++ b/mercurial/pycompat.py
@@ -45,6 +45,7 @@ if ispy3:
     ospathsep = os.pathsep.encode('ascii')
     ossep = os.sep.encode('ascii')
     osaltsep = os.altsep
+    osgetenv = os.getenvb
     if osaltsep:
         osaltsep = osaltsep.encode('ascii')
     # os.getcwd() on Python 3 returns string, but it has os.getcwdb() which
@@ -156,6 +157,7 @@ else:
     sysargv = sys.argv
     sysplatform = sys.platform
     getcwd = os.getcwd
+    osgetenv = os.getenv
 
 stringio = io.StringIO
 empty = _queue.Empty