diff --git a/appveyor.yml b/appveyor.yml
index 86b7a87db7..d13ec885d1 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -5,7 +5,7 @@ platform:
   - x64
 environment:
   ruby_version: "24-%Platform%"
-  zlib_version: "1.2.12"
+  zlib_version: "1.2.13"
   matrix:
     - build: vs
       vs: 120