diff --git a/stack.yaml b/stack.yaml
index b06bc4d..1efd91f 100644
--- a/stack.yaml
+++ b/stack.yaml
@@ -15,7 +15,7 @@
 # resolver:
 #  name: custom-snapshot
 #  location: "./custom-snapshot.yaml"
-resolver: lts-11.9
+resolver: lts-12.9
 
 # User packages to be built.
 # Various formats can be used as shown in the example below.
@@ -41,7 +41,7 @@ packages:
 - '../zeromq4-haskell-zap'
 # Dependency packages to be pulled from upstream that are not in the resolver
 # (e.g., acme-missiles-0.3)
-extra-deps: [ "datetime-0.3.1" ]
+extra-deps: [ "datetime-0.3.1", "text-format-0.3.2" ]
 
 # Override default flag values for local packages and extra-deps
 flags: {}