diff --git a/.github/workflows/check-prompts.yml b/.github/workflows/check-prompts.yml
index bed49f3..3505bba 100644
--- a/.github/workflows/check-prompts.yml
+++ b/.github/workflows/check-prompts.yml
@@ -57,6 +57,17 @@ jobs:
       - name: Run prompt check
         run: bash scripts/check-prompts.sh
 
+  check-prompts-macos:
+    name: Prompt metadata check (macOS Bash 3.2)
+    runs-on: macos-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Run prompt check with system Bash
+        run: /bin/bash scripts/check-prompts.sh
+
   check-docs:
     name: Docs consistency check
     runs-on: ubuntu-latest
diff --git a/scripts/check-prompts.sh b/scripts/check-prompts.sh
index 5c6fc42..ed668c9 100755
--- a/scripts/check-prompts.sh
+++ b/scripts/check-prompts.sh
@@ -133,7 +133,7 @@ fi
 echo ""
 echo "[ mode coverage ]"
 while IFS= read -r mode_name; do
-  mode_id="${mode_name,,}"
+  mode_id="$(printf '%s' "$mode_name" | tr '[:upper:]' '[:lower:]')"
   if [[ -f "$MODES_DIR/$mode_id.md" ]]; then
     ok "$mode_id.md exists"
   else