diff --git a/.github/workflows/windows-nightly.yml b/.github/workflows/windows-nightly.yml
index 0c20850b3..5d6d29179 100644
--- a/.github/workflows/windows-nightly.yml
+++ b/.github/workflows/windows-nightly.yml
@@ -52,9 +52,8 @@ jobs:
         #key: ${{ runner.os }}-appdata-local-programs-stack-${{ github.sha }}
         # which files signal a change in the global stack dir ?
         # 'stack.yaml','stack.lock' should be included, but how
-        key: ${{ runner.os }}-appdata-local-programs-stack-${{ '*/*.cabal' }}
-        restore-keys: |
-             ${{ runner.os }}-appdata-local-programs-stack-
+        key:          ${{ runner.os }}-appdata-local-programs-stack-${{ hashFiles('*/*.cabal') }}
+        restore-keys: ${{ runner.os }}-appdata-local-programs-stack-
     - name: Cache C:\Users\runneradmin\AppData\Local\Packages\
       uses: actions/cache@v1
       with: