diff --git a/stack.yaml b/stack.yaml
index 3a341ec..a58ab92 100644
--- a/stack.yaml
+++ b/stack.yaml
@@ -5,4 +5,4 @@ flags:
 packages:
 - '.'
 extra-deps: [markdown-0.1.13.2,../geval,cond-0.4.1.1,wai-handler-fastcgi-3.0.0.2,murmur3-1.0.3,extra-1.4.10]
-resolver: lts-9.14
+resolver: lts-9.21