diff --git a/tests/flask_tests.py b/tests/flask_tests.py
index 04b547776b..46455e99a0 100644
--- a/tests/flask_tests.py
+++ b/tests/flask_tests.py
@@ -47,6 +47,10 @@ def has_encoding(name):
 def catch_warnings():
     """Catch warnings in a with block in a list"""
     import warnings
+
+    # make sure deprecation warnings are active in tests
+    warnings.simplefilter('default', category=DeprecationWarning)
+
     filters = warnings.filters
     warnings.filters = filters[:]
     old_showwarning = warnings.showwarning