diff --git a/compose.yml b/compose.yml
index 0a05210..06fda6e 100644
--- a/compose.yml
+++ b/compose.yml
@@ -1,6 +1,6 @@
 services:
   dev:
-    image: ghcr.io/flipstone/haskell-tools:debian-unstable-ghc-9.4.5-2023-07-18-1d8bf61
+    image: ghcr.io/flipstone/haskell-tools:debian-stable-ghc-9.4.6-2023-08-29-52330cd
     environment:
       STACK_ROOT: /stack-root
       IN_DEV_CONTAINER: 'true'
diff --git a/stack.yaml b/stack.yaml
index 590cd22..14e4bb6 100644
--- a/stack.yaml
+++ b/stack.yaml
@@ -1,4 +1,4 @@
-resolver: lts-21.3
+resolver: lts-21.9
 system-ghc: true
 install-ghc: false
 
diff --git a/stack.yaml.lock b/stack.yaml.lock
index f587b6e..6b7208c 100644
--- a/stack.yaml.lock
+++ b/stack.yaml.lock
@@ -6,7 +6,7 @@
 packages: []
 snapshots:
 - completed:
-    sha256: 97710f56bf093fca0ee5d8dbe19d96b654c752e405b66795b4baedd84a794c60
-    size: 640010
-    url: https://raw.githubusercontent.com/commercialhaskell/stackage-snapshots/master/lts/21/3.yaml
-  original: lts-21.3
+    sha256: 2fc12a405ab6f7eac73eb11a0ca5ccca0e956bd2848db780c140b7406ff9ebb5
+    size: 640035
+    url: https://raw.githubusercontent.com/commercialhaskell/stackage-snapshots/master/lts/21/9.yaml
+  original: lts-21.9