diff --git a/Libraries/zlib/files/variants.rhel6 b/Libraries/zlib/files/variants.rhel6
index 547fb5e..508ca7e 100644
--- a/Libraries/zlib/files/variants.rhel6
+++ b/Libraries/zlib/files/variants.rhel6
@@ -1 +1,2 @@
 zlib/1.2.11	stable
+zlib/1.2.13	unstable