diff --git a/src/olympia/blocklist/mlbf.py b/src/olympia/blocklist/mlbf.py
index d0814eb9d79..868e87f50fb 100644
--- a/src/olympia/blocklist/mlbf.py
+++ b/src/olympia/blocklist/mlbf.py
@@ -150,12 +150,13 @@ def blocked_items(self) -> List[str]:
     def not_blocked_items(self) -> List[str]:
         # see blocked_items - we need self._version_excludes populated
         blocked_items = self.blocked_items
+        not_blocked_items = MLBF.hash_filter_inputs(
+            fetch_all_versions_from_db(self._version_excludes)
+        )
         # even though we exclude all the version ids in the query there's an
         # edge case where the version string occurs twice for an addon so we
         # ensure not_blocked_items doesn't contain any blocked_items.
-        return MLBF.hash_filter_inputs(
-            fetch_all_versions_from_db(self._version_excludes) - set(blocked_items)
-        )
+        return list(set(not_blocked_items) - set(blocked_items))
 
 
 class MLBF:
diff --git a/src/olympia/blocklist/tests/test_mlbf.py b/src/olympia/blocklist/tests/test_mlbf.py
index 9298778c6a3..e9026f69976 100644
--- a/src/olympia/blocklist/tests/test_mlbf.py
+++ b/src/olympia/blocklist/tests/test_mlbf.py
@@ -1,6 +1,8 @@
 import json
 from functools import cached_property
 
+from olympia import amo
+from olympia.addons.models import GUID_REUSE_FORMAT
 from olympia.amo.tests import (
     TestCase,
     addon_factory,
@@ -351,3 +353,30 @@ def test_generate_filter_not_raises_if_all_versions_blocked(self):
         self._blocked_addon(file_kw={'is_signed': False})
         assert mlbf.data.not_blocked_items == []
         mlbf.generate_and_write_filter()
+
+    def test_duplicate_guid_is_blocked(self):
+        """
+        Test that if there are addons with duplicated guids, and one is blocked,
+        the addon should be blocked and the other should not be included in not_blocked
+        """
+        version = '2.1'
+        reused_addon = addon_factory(
+            status=amo.STATUS_DELETED,
+            version_kw={'version': version},
+            file_kw={'is_signed': True},
+        )
+        addon, block = self._blocked_addon(
+            version_kw={'version': version},
+            file_kw={'is_signed': True},
+        )
+
+        reused_addon.update(guid=GUID_REUSE_FORMAT.format(addon.id))
+        reused_addon.addonguid.update(guid=addon.guid)
+
+        self._block_version(block, self._version(addon), soft=False)
+
+        mlbf = MLBF.generate_from_db('test')
+
+        (block_version,) = MLBF.hash_filter_inputs([(addon.guid, version)])
+        assert block_version in mlbf.data.blocked_items
+        assert block_version not in mlbf.data.not_blocked_items