diff --git a/.github/scripts/assert-version.sh b/.github/scripts/assert-version.sh
new file mode 100644
index 0000000..516b250
--- /dev/null
+++ b/.github/scripts/assert-version.sh
@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+# Usage: ./assert-version.sh <package-name> <expected-version>
+
+set -euo pipefail
+
+PKG="$1"
+EXPECTED="$2"
+FREEZE_FILE="cabal.project.freeze"
+
+cabal freeze -v0
+[[ -f "$FREEZE_FILE" ]] || { echo "Error: Missing freeze file"; exit 1; }
+
+if grep -q "any.$PKG ==$EXPECTED" "$FREEZE_FILE"; then
+  echo "Assertion passed: $PKG's version is $EXPECTED"
+  rm "$FREEZE_FILE"
+else
+  echo "Assertion failed: $PKG's version is NOT $EXPECTED"
+  cat "$FREEZE_FILE" | grep "any.$PKG"
+  rm "$FREEZE_FILE"
+  exit 1
+fi
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 79e6606..ede3e5c 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -40,6 +40,11 @@ jobs:
 
       - uses: actions/checkout@v3
 
+      - name: Add scripts to GITHUB_PATH
+        run: |
+          chmod +x .github/scripts/*
+          echo "${{ github.workspace }}/.github/scripts" >> $GITHUB_PATH
+
       - name: Set up GHC and Cabal
         uses: haskell-actions/setup@v2
         with:
@@ -56,11 +61,17 @@ jobs:
 
       - name: Import Stackage snapshot
         run: |
-          echo "import: https://www.stackage.org/${{ matrix.stackage }}/cabal.config" >> cabal.project.local
+          LOCAL_CONFIG="stackage-local.config"
+          curl -sSL https://www.stackage.org/${{ matrix.stackage }}/cabal.config > $LOCAL_CONFIG
+
+          # Remove any existing constraint on this package from the Stackage snapshot.
+          sed -i "/^[[:space:]]*json-rpc-server[[:space:]]*==/d" $LOCAL_CONFIG
+
+          echo "import: $LOCAL_CONFIG" >> cabal.project.local
 
-      - name: Constrain aeson version
+      - name: Assert aeson version
         run: |
-          echo "constraints: aeson==${{ matrix.aeson }}" >> cabal.project.local
+          assert-version.sh aeson "${{ matrix.aeson }}"
 
       - name: Install dependencies
         run: cabal v2-build --only-dependencies --enable-tests
@@ -80,13 +91,14 @@ jobs:
       - name: Verify that sdist installs
         run: |
           SDIST=$(grep '^version:' json-rpc-server.cabal | awk '{print "json-rpc-server-" $2 ".tar.gz"}')
-          cp cabal.project.local dist-newstyle/sdist/
+          cp cabal.project.local stackage-local.config dist-newstyle/sdist/
           cd dist-newstyle/sdist/
           if [ -f "$SDIST" ]; then
             tar xzf "$SDIST"
             PKGDIR=$(basename "$SDIST" .tar.gz)
-            mv cabal.project.local "$PKGDIR"
+            mv cabal.project.local stackage-local.config "$PKGDIR"
             cd "$PKGDIR"
+            assert-version.sh aeson "${{ matrix.aeson }}"
             cabal v2-build all
           else
             echo "expected '$SDIST' not found"