diff --git a/hgext/git/__init__.py b/hgext/git/__init__.py
index 250e18437e30820f449a2cc807b6909e309fbd4c_aGdleHQvZ2l0L19faW5pdF9fLnB5..a001e28ad5eb4ffb52a61f2371f64445cc918b5d_aGdleHQvZ2l0L19faW5pdF9fLnB5 100644
--- a/hgext/git/__init__.py
+++ b/hgext/git/__init__.py
@@ -29,6 +29,12 @@
     index,
 )
 
+# Note for extension authors: ONLY specify testedwith = 'ships-with-hg-core' for
+# extensions which SHIP WITH MERCURIAL. Non-mainline extensions should
+# be specifying the version(s) of Mercurial they are tested with, or
+# leave the attribute unspecified.
+testedwith = b'ships-with-hg-core'
+
 configtable = {}
 configitem = registrar.configitem(configtable)
 # git.log-index-cache-miss: internal knob for testing