diff --git a/jtl-wafi-agent.py b/jtl-wafi-agent.py
index 50d37e4..97eeb74 100644
--- a/jtl-wafi-agent.py
+++ b/jtl-wafi-agent.py
@@ -31,6 +31,7 @@ import ipaddress
 import signal
 import platform
 import threading
+import fcntl
 import urllib.request
 import urllib.error
 from datetime import datetime, timedelta, timezone
@@ -2596,13 +2597,6 @@ def add_shop_to_active(shop: str,
         monitor_only: Nur Monitoring, kein Blocking
     """
     os.makedirs(os.path.dirname(ACTIVE_SHOPS_FILE), exist_ok=True)
-    shops = {}
-    if os.path.isfile(ACTIVE_SHOPS_FILE):
-        try:
-            with open(ACTIVE_SHOPS_FILE, 'r') as f:
-                shops = json.load(f)
-        except:
-            shops = {}
 
     shop_data = {
         "activated": datetime.now().isoformat(),
@@ -2623,24 +2617,49 @@ def add_shop_to_active(shop: str,
     if unlimited_countries:
         shop_data["unlimited_countries"] = unlimited_countries
 
-    shops[shop] = shop_data
-    with open(ACTIVE_SHOPS_FILE, 'w') as f:
-        json.dump(shops, f, indent=2)
+    # File Locking für sichere parallele Zugriffe
+    lock_file = ACTIVE_SHOPS_FILE + '.lock'
+    with open(lock_file, 'w') as lf:
+        fcntl.flock(lf, fcntl.LOCK_EX)  # Exklusiver Lock - wartet wenn gesperrt
+        try:
+            shops = {}
+            if os.path.isfile(ACTIVE_SHOPS_FILE):
+                try:
+                    with open(ACTIVE_SHOPS_FILE, 'r') as f:
+                        shops = json.load(f)
+                except:
+                    shops = {}
+
+            shops[shop] = shop_data
+
+            with open(ACTIVE_SHOPS_FILE, 'w') as f:
+                json.dump(shops, f, indent=2)
+        finally:
+            fcntl.flock(lf, fcntl.LOCK_UN)  # Lock freigeben
 
 
 def remove_shop_from_active(shop: str):
     """Entfernt einen Shop aus der aktiven Liste."""
     if not os.path.isfile(ACTIVE_SHOPS_FILE):
         return
-    try:
-        with open(ACTIVE_SHOPS_FILE, 'r') as f:
-            shops = json.load(f)
-        if shop in shops:
-            del shops[shop]
-        with open(ACTIVE_SHOPS_FILE, 'w') as f:
-            json.dump(shops, f, indent=2)
-    except:
-        pass
+
+    # File Locking für sichere parallele Zugriffe
+    lock_file = ACTIVE_SHOPS_FILE + '.lock'
+    with open(lock_file, 'w') as lf:
+        fcntl.flock(lf, fcntl.LOCK_EX)  # Exklusiver Lock - wartet wenn gesperrt
+        try:
+            if not os.path.isfile(ACTIVE_SHOPS_FILE):
+                return
+            with open(ACTIVE_SHOPS_FILE, 'r') as f:
+                shops = json.load(f)
+            if shop in shops:
+                del shops[shop]
+            with open(ACTIVE_SHOPS_FILE, 'w') as f:
+                json.dump(shops, f, indent=2)
+        except:
+            pass
+        finally:
+            fcntl.flock(lf, fcntl.LOCK_UN)  # Lock freigeben
 
 
 def get_shop_config(shop: str) -> Dict[str, Any]: