diff --git a/setup.cfg b/setup.cfg
index b736709d..b7dc04bb 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -36,7 +36,7 @@ install_requires =
     Flask-SQLAlchemy~=2.4
     Flask-WTF~=0.14,>=0.14.3  # See b76da172652da94c1f9c4b2fdd965375da8a2c3f
     WTForms~=2.2.1,<2.3  # See #567
-    Flask~=1.1
+    Flask>=1.1,<3.0
     itsdangerous~=1.1
     Jinja2~=2.11
     requests~=2.22