diff --git a/wanda/as_filter/as_filter.py b/wanda/as_filter/as_filter.py
index 658d998..09a9f68 100644
--- a/wanda/as_filter/as_filter.py
+++ b/wanda/as_filter/as_filter.py
@@ -1,4 +1,5 @@
 import re
+from functools import cached_property
 
 from wanda.autonomous_system.autonomous_system import AutonomousSystem
 from wanda.irrd_client import IRRDClient
@@ -9,12 +10,13 @@
 
 class ASFilter:
 
-    def __init__(self, irrd_client: IRRDClient, autos: AutonomousSystem, enable_extended_filters=False):
+    def __init__(self, irrd_client: IRRDClient, autos: AutonomousSystem, is_customer=True):
         self.irrd_client = irrd_client
         self.autos = autos
-        self.enable_extended_filters = enable_extended_filters
+        self.is_customer = is_customer
 
-    def get_prefix_lists(self):
+    @cached_property
+    def prefix_lists(self):
 
         v4_set = set()
         v6_set = set()
@@ -27,14 +29,14 @@ def get_prefix_lists(self):
             v4_set.update(result_entries_v4_cleaned)
             v6_set.update(result_entries_v6_cleaned)
 
-        if len(v4_set) == 0 and len(v6_set) == 0:
+        if len(v4_set) == 0 and len(v6_set) == 0 and self.is_customer:
             l.error(f"{self.autos} has no v4 filter lists.")
             raise Exception(
                 f"{self.autos} has no v6 filter lists. Since AS is our customer, we forbid this for security reasons.")
 
         return v4_set, v6_set
 
-    def get_filter_lists(self):
+    def get_filter_lists(self, enable_extended_filters=False):
 
         irr_names = self.autos.get_irr_names()
         file_content = self.irrd_client.generate_input_aspath_access_list(self.autos.asn, irr_names[0])
@@ -43,8 +45,8 @@ def get_filter_lists(self):
             l.warning(f"{self.autos} could not generate as-path access-lists, this breaks configuration syntax..")
             return ""
 
-        if self.enable_extended_filters:
-            v4_set, v6_set = self.get_prefix_lists()
+        if enable_extended_filters:
+            v4_set, v6_set = self.prefix_lists
 
             v4_tmpl = ';\n    '.join(sorted(v4_set))
             v6_tmpl = ';\n    '.join(sorted(v6_set))
diff --git a/wanda/filter_list_generation.py b/wanda/filter_list_generation.py
index 811f518..99a2eba 100644
--- a/wanda/filter_list_generation.py
+++ b/wanda/filter_list_generation.py
@@ -11,11 +11,12 @@
 def process_filter_lists_for_as(arg):
     [irrd_client, autonomous_system, customer_as, filter_lists] = arg
     asn = autonomous_system.asn
+    is_customer = asn in customer_as
 
-    extended_filtering = asn in customer_as
-
-    ass = ASFilter(irrd_client, autonomous_system, enable_extended_filters=extended_filtering)
-    as_filter_list = ass.get_filter_lists()
+    ass = ASFilter(irrd_client, autonomous_system, is_customer=is_customer)
+    v4_set, v6_set = ass.prefix_lists
+    extended_filtering = is_customer or len(v4_set) + len(v6_set) < 5000
+    as_filter_list = ass.get_filter_lists(enable_extended_filters=extended_filtering)
 
     filter_lists[asn] = as_filter_list
 
diff --git a/wanda/tests/test_as_filter.py b/wanda/tests/test_as_filter.py
index cef1302..41c0756 100644
--- a/wanda/tests/test_as_filter.py
+++ b/wanda/tests/test_as_filter.py
@@ -55,13 +55,15 @@ def get_asfilter(**kwargs):
 class TestASFilter:
 
     @pytest.mark.parametrize(
-        "asfilter,enable_extended_filters",
+        "enable_extended_filters",
         [
-            (get_asfilter(enable_extended_filters=True), True),
-            (get_asfilter(enable_extended_filters=False), False)
+            (True),
+            (False)
         ]
     )
-    def test_prefix_lists(self, mocker, asfilter, enable_extended_filters):
+    def test_prefix_lists(self, mocker, enable_extended_filters):
+        asfilter = get_asfilter()
+
         mocker.patch(
             'wanda.irrd_client.IRRDClient.generate_prefix_lists',
             return_value=(WOBCOM_PREFIX_LIST_MOCK_V4, WOBCOM_PREFIX_LIST_MOCK_V6)
@@ -72,7 +74,7 @@ def test_prefix_lists(self, mocker, asfilter, enable_extended_filters):
             return_value=AS_PATH_MOCK
         )
 
-        file_content = asfilter.get_filter_lists()
+        file_content = asfilter.get_filter_lists(enable_extended_filters)
 
         assert len(file_content) > 0