diff --git a/.appveyor.yml b/.appveyor.yml
index 1ea5e59210..5fb678c3c6 100644
--- a/.appveyor.yml
+++ b/.appveyor.yml
@@ -19,7 +19,7 @@ skip_commits:
     - '**/.document'
 environment:
   ruby_version: "24-%Platform%"
-  zlib_version: "1.2.12"
+  zlib_version: "1.2.13"
   matrix:
     - build: vs
       vs: 120