diff --git a/requirements/constraints.txt b/requirements/constraints.txt
index 78dfaff1ae..a4e8ffc786 100644
--- a/requirements/constraints.txt
+++ b/requirements/constraints.txt
@@ -57,6 +57,9 @@ httpretty<1.0
 # 4.0.0 dropped support for Python 3.5
 inflect<4.0.0
 
+# 5.0.0 dropped support for Python 3.5
+isort<5.0.0
+
 # 0.15.0 dropped support for Python 3.5
 joblib<0.15.0