diff --git a/requirements.txt b/requirements.txt
index 0a7f2e86011..6c978246214 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,6 +1,6 @@
 # GRPC Python setup requirements
 coverage>=4.0
-cython>=0.27
+cython==0.28.3
 enum34>=1.0.4
 protobuf>=3.5.0.post1
 six>=1.10