diff --git a/tests/requirements.txt b/tests/requirements.txt
index db0fdfe..b356e07 100644
--- a/tests/requirements.txt
+++ b/tests/requirements.txt
@@ -1,7 +1,7 @@
 coverage==4.4.1
 flake8==3.4.0
 isort==4.2.15
-mypy==0.520
+mypy==0.521
 pycodestyle==2.3.1
 pyflakes==1.5.0
 pytest==3.1.3