diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index ccab7e1c..f9a6d50a 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -43,6 +43,7 @@ jobs:
           - stack-yaml: 'stack-8.6.yaml'
           - stack-yaml: 'stack-8.8.yaml'
           - stack-yaml: 'stack.yaml'
+          - stack-yaml: 'stack-9.0.yaml'
 
     steps:
       - uses: actions/checkout@v2
diff --git a/src/IHaskell/Eval/Util.hs b/src/IHaskell/Eval/Util.hs
index 83ed6485..dea936d5 100644
--- a/src/IHaskell/Eval/Util.hs
+++ b/src/IHaskell/Eval/Util.hs
@@ -265,7 +265,8 @@ setFlags ext = do
 #else
       allWarns = map unLoc warnings ++
 #endif
-                 ["-package not supported yet" | packageFlags flags /= packageFlags flags0]
+        -- Stack appears to duplicate package flags, so we use `nub` to work around this
+        ["-package not supported yet" | nub (packageFlags flags) /= nub (packageFlags flags0)]
       warnErrs = map ("Warning: " ++) allWarns
   return $ noParseErrs ++ warnErrs
 
diff --git a/stack-lts19.yaml b/stack-9.0.yaml
similarity index 98%
rename from stack-lts19.yaml
rename to stack-9.0.yaml
index ca890244..b547be2b 100644
--- a/stack-lts19.yaml
+++ b/stack-9.0.yaml
@@ -1,5 +1,5 @@
 # the GHC version of this resolver needs to match the GHC version in Dockerfile
-resolver: lts-19.3
+resolver: lts-19.10
 #allow-newer: true
 
 flags: {}