diff --git a/.appveyor.yml b/.appveyor.yml
index 1f179143c8..c8bf89e0d6 100644
--- a/.appveyor.yml
+++ b/.appveyor.yml
@@ -18,7 +18,7 @@ skip_commits:
     - '**/*.rdoc'
 environment:
   ruby_version: "24-%Platform%"
-  zlib_version: "1.2.11"
+  zlib_version: "1.2.12"
   matrix:
     - build: vs
       vs: 120