diff --git a/requirements-dev.txt b/requirements-dev.txt
index b80a32e422..600d4f4012 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -3,4 +3,5 @@ pytest-cov
 pytest-httpbin<1.0
 pytest-mock==2.0.0
 httpbin==0.7.0
+Flask>=1.0,<2.0
 wheel