diff --git a/requirements.txt b/requirements.txt
index fa9f5fb96816092841bd88e5b03692bb1e7c5663..8cc8a0e8018f98d56ba84fdda652438860425582 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -64,7 +64,9 @@ ipaddress
 
 # {{{ For interoperation with SAML2/Shibboleth
 
-pysaml2==4.6.1
+# 4.6.1 suffers from https://github.com/IdentityPython/pysaml2/pull/543
+# 4.6.5 causes a 403 on /saml2/acs upon sign in with djangosaml2
+pysaml2==4.6.0
 djangosaml2==0.17.2
 python-memcached