diff --git a/test-constraints.txt b/test-constraints.txt
index 815716c06..7a2acccf2 100644
--- a/test-constraints.txt
+++ b/test-constraints.txt
@@ -1 +1,3 @@
 soupsieve < 2.0; python_version < '3.5'
+# oauthlib 3.1.1 supports only py > 3.5
+oauthlib < 3.1.1;python_version < '3.6'