diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 03372c26..82f4220d 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -30,6 +30,9 @@ jobs:
       # @link https://github.com/marketplace/actions/install-composer-dependencies
       - name: Install Composer dependencies
         uses: "ramsey/composer-install@v2"
+        with:
+          # Bust the cache at least once a month - output format: YYYY-MM-DD.
+          custom-cache-suffix: $(date -u -d "-0 month -$(($(date +%d)-1)) days" "+%F")
 
       - name: Check coding standards
         id: phpcs
@@ -67,6 +70,9 @@ jobs:
       # @link https://github.com/marketplace/actions/install-composer-dependencies
       - name: Install Composer dependencies
         uses: "ramsey/composer-install@v2"
+        with:
+          # Bust the cache at least once a month - output format: YYYY-MM-DD.
+          custom-cache-suffix: $(date -u -d "-0 month -$(($(date +%d)-1)) days" "+%F")
 
       - name: Lint against parse errors
         if: ${{ matrix.php != '8.2' }}
@@ -119,12 +125,17 @@ jobs:
       - name: Install PHP packages - normal
         if: ${{ matrix.php != '8.2' }}
         uses: "ramsey/composer-install@v2"
+        with:
+          # Bust the cache at least once a month - output format: YYYY-MM-DD.
+          custom-cache-suffix: $(date -u -d "-0 month -$(($(date +%d)-1)) days" "+%F")
 
       - name: Install PHP packages - ignore-platform-reqs
         if: ${{ matrix.php == '8.2' }}
         uses: "ramsey/composer-install@v2"
         with:
           composer-options: --ignore-platform-reqs
+          # Bust the cache at least once a month - output format: YYYY-MM-DD.
+          custom-cache-suffix: $(date -u -d "-0 month -$(($(date +%d)-1)) days" "+%F")
 
       # Install postfix and automatically retry if the install failed, which happens reguarly.
       # @link https://github.com/marketplace/actions/retry-step