diff --git a/.circleci/config.yml b/.circleci/config.yml
index df7bc1b..842b76c 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -57,7 +57,7 @@ jobs:
   build_nightly:
     <<: *stack_build
     environment:
-      STACK_ARGUMENTS: --stack-yaml stack-nightly.yaml
+      STACK_ARGUMENTS: --resolver nightly --stack-yaml stack-nightly.yaml
 
 workflows:
   version: 2
diff --git a/stack-nightly.yaml b/stack-nightly.yaml
index 13c4951..f4b49dc 100644
--- a/stack-nightly.yaml
+++ b/stack-nightly.yaml
@@ -1,4 +1,7 @@
 ---
-resolver: nightly
+# You can't use "nightly" here, only "nightly-<date>", apparently. But you
+# can't leave it blank either, so here's a value that we'll override by
+# --resolver nightly.
+resolver: lts-11.5
 extra-deps:
   - hoauth2-1.7.1