diff --git a/stretch/preferences.d/entrouvert-debian-backports b/stretch/preferences.d/entrouvert-debian-backports
index ea525e3..e6f9927 100644
--- a/stretch/preferences.d/entrouvert-debian-backports
+++ b/stretch/preferences.d/entrouvert-debian-backports
@@ -17,6 +17,11 @@ Package: python-attr
 Pin: release a=stretch-backports
 Pin-Priority: 900
 
+# python-cryptography, >= 1.9 indirectly required for combo (push notifications)
+Package: python-cryptography
+Pin: release a=stretch-backports
+Pin-Priority: 900
+
 #
 # certbot packages
 #