diff --git a/.forgejo/workflows/ci.yml b/.forgejo/workflows/ci.yml
index 05f77f3..299224e 100644
--- a/.forgejo/workflows/ci.yml
+++ b/.forgejo/workflows/ci.yml
@@ -16,17 +16,63 @@ jobs:
       - uses: actions/checkout@v4
 
       - id: filter
-        uses: dorny/paths-filter@v3
-        with:
-          filters: |
-            backend:
-              - 'back001/**'
-              - '.forgejo/workflows/**'
-              - 'ci/**'
-            frontend:
-              - 'front001/**'
-              - '.forgejo/workflows/**'
-              - 'ci/**'
+        name: Detect changes
+        run: |
+          python - <<'PY'
+          import json
+          import os
+          import subprocess
+          import sys
+
+          event_path = os.environ.get("GITHUB_EVENT_PATH")
+          base = None
+          head = None
+          if event_path and os.path.exists(event_path):
+            with open(event_path, "r", encoding="utf-8") as handle:
+              data = json.load(handle)
+            if "pull_request" in data:
+              base = data["pull_request"]["base"]["sha"]
+              head = data["pull_request"]["head"]["sha"]
+            else:
+              base = data.get("before")
+              head = data.get("after") or data.get("checkout_sha")
+
+          if not head:
+            head = os.environ.get("GITHUB_SHA")
+
+          if not base or base == "0000000000000000000000000000000000000000":
+            try:
+              subprocess.check_call(
+                ["git", "rev-parse", f"{head}^"],
+                stdout=subprocess.DEVNULL,
+                stderr=subprocess.DEVNULL,
+              )
+              base = f"{head}^"
+            except Exception:
+              base = None
+
+          if base:
+            diff_cmd = ["git", "diff", "--name-only", base, head]
+          else:
+            diff_cmd = ["git", "ls-files"]
+
+          files = subprocess.check_output(diff_cmd, text=True).splitlines()
+          backend = False
+          frontend = False
+          for path in files:
+            if path.startswith("back001/") or path.startswith(".forgejo/workflows/") or path.startswith("ci/"):
+              backend = True
+            if path.startswith("front001/") or path.startswith(".forgejo/workflows/") or path.startswith("ci/"):
+              frontend = True
+
+          out_path = os.environ.get("GITHUB_OUTPUT")
+          if not out_path:
+            print("GITHUB_OUTPUT not set", file=sys.stderr)
+            sys.exit(1)
+          with open(out_path, "a", encoding="utf-8") as handle:
+            handle.write(f"backend={'true' if backend else 'false'}\n")
+            handle.write(f"frontend={'true' if frontend else 'false'}\n")
+          PY
     outputs:
       backend: ${{ steps.filter.outputs.backend }}
       frontend: ${{ steps.filter.outputs.frontend }}