diff --git a/stack.pkg.yaml b/stack.pkg.yaml
index a5fe42d27..d9de4fdd9 100644
--- a/stack.pkg.yaml
+++ b/stack.pkg.yaml
@@ -24,4 +24,4 @@ extra-deps:
 - tasty-quickcheck-0.9.1
 - haddock-library-1.4.3
 - pandoc-types-1.17.1
-resolver: lts-9.0
+resolver: lts-9.1
diff --git a/stack.yaml b/stack.yaml
index e348ce4c1..6e94971a8 100644
--- a/stack.yaml
+++ b/stack.yaml
@@ -14,4 +14,4 @@ extra-deps:
 - tasty-quickcheck-0.9.1
 - haddock-library-1.4.3
 - pandoc-types-1.17.1
-resolver: lts-9.0
+resolver: lts-9.1