diff --git a/tests/requirements.txt b/tests/requirements.txt
index 0fe5eda..7d70229 100644
--- a/tests/requirements.txt
+++ b/tests/requirements.txt
@@ -1,6 +1,6 @@
 black==19.10b0
 coverage==5.1
-Cython==0.29.20;sys_platform!='win32'
+Cython==0.29.21;sys_platform!='win32'
 flake8==3.8.3
 flake8-quotes==3.2.0
 isort==4.3.21