diff --git a/requirements/build.in b/requirements/build.in
index 1de8dc58818b5e7f0df14e79810fd97bc97d5bd2..c95cbff797db8656465ad825943b4704db1bc340 100644
--- a/requirements/build.in
+++ b/requirements/build.in
@@ -23,6 +23,6 @@ docutils>=0.17
 identify>=2.2.2
 pygments>=2.8.1
 pytz>=2020.5
-Flask>=1.1.2
+Flask>=1.1.4,<2.0
 Flask-SQLAlchemy>=2.5.1
 SQLAlchemy>=1.4.15
\ No newline at end of file