diff --git a/urllib3/dev-requirements.txt b/urllib3/dev-requirements.txt
index 18837f998..8ac2f33b2 100644
--- a/urllib3/dev-requirements.txt
+++ b/urllib3/dev-requirements.txt
@@ -1,7 +1,7 @@
 mock==3.0.5
 coverage~=4.5
 tornado==5.1.1;python_version<="2.7"
-tornado==6.0.3;python_version>="3.5"
+tornado==6.3.3;python_version>="3.5"
 PySocks==1.7.1
 # https://github.com/Anorov/PySocks/issues/131
 win-inet-pton==1.1.0