diff --git a/.github/workflows/dev.yml b/.github/workflows/dev.yml
index 6920f64..1258d77 100644
--- a/.github/workflows/dev.yml
+++ b/.github/workflows/dev.yml
@@ -15,25 +15,40 @@ jobs:
         - releases/v0.21
     steps:
     - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11
+
     - name: Set up Spack
       uses: ./
       with:
         ref: ${{ matrix.ref }}
         buildcache: true
         color: true
+
     - name: Version check
       run: spack --version
+
     - name: Check build cache config
       run: spack config blame mirrors
-    - name: Check build cache install in active env with spack-bash shell
+
+    - name: Check build cache install in active env with spack-bash shell (new style)
       shell: spack-bash {0}
       run: |
         spack env activate
-        spack install --add --cache-only --no-check-signature --reuse python
+        spack install --add --cache-only --reuse python
         which python3
         python3 -c 'print("hello world")'
+      if: matrix.ref == 'develop'
+
+    - name: Check build cache install in active env with spack-bash shell (old style)
+      shell: spack-bash {0}
+      run: |
+        spack env activate
+        spack install --add --cache-only --reuse --no-check-signature python
+        which python3
+        python3 -c 'print("hello world")'
+      if: matrix.ref == 'develop'
+
     - name: Check spack-sh shell
       shell: spack-sh {0}
       run: |
         spack env activate
-        spack env status
\ No newline at end of file
+        spack env status
diff --git a/README.md b/README.md
index 7a4f71e..5ed8f24 100644
--- a/README.md
+++ b/README.md
@@ -17,13 +17,20 @@ jobs:
         buildcache: true  # Configure oci://ghcr.io/spack/github-actions-buildcache
         color: true       # Force color output (SPACK_COLOR=always)
         path: spack       # Where to clone Spack
-    - run: spack install --no-check-signature --reuse python
+    - run: spack install python
 ```
 
 When `buildcache: true` is set, binaries from https://github.com/spack/github-actions-buildcache
 are used. For available software, [see here](https://github.com/spack/github-actions-buildcache/blob/main/spack.yaml).
 
-These binaries are unsigned, so you have to specify `install --no-check-signature`.
+**Note**: when using the build cache with Spack v0.21 and below, the following flag is
+required:
+
+```
+spack install --no-check-signature
+```
+
+This flag is no longer required in Spack v0.22.
 
 ## Example: shell support
 
diff --git a/action.yml b/action.yml
index 32b16c0..c5027cd 100644
--- a/action.yml
+++ b/action.yml
@@ -40,6 +40,8 @@ runs:
   - name: Spack configuration
     run: |
       if [ ${{ inputs.buildcache }} = "true" ]; then
+        # Spack 0.22 should support the --unsigned flag
+        spack mirror add --unsigned github-actions-buildcache oci://ghcr.io/spack/github-actions-buildcache || \
         spack mirror add github-actions-buildcache oci://ghcr.io/spack/github-actions-buildcache
       fi
     shell: sh