diff --git a/pip/_internal/vcs/mercurial.py b/pip/_internal/vcs/mercurial.py
index d9b58cf..4747cf6 100644
--- a/pip/_internal/vcs/mercurial.py
+++ b/pip/_internal/vcs/mercurial.py
@@ -38,7 +38,7 @@ class Mercurial(VersionControl):
 
     @staticmethod
     def get_base_rev_args(rev):
-        return [rev]
+        return ["--rev={}".format(rev)]
 
     def export(self, location, url):
         # type: (str, HiddenText) -> None