diff --git a/CHANGELOG.md b/CHANGELOG.md
index f7adefabb93febaf364133d0647fde5b0e535d0a..e98dece18716f6a1034a9987caa7d38afa72837c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,6 +16,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Removed ###
 
 ### Fixed ###
+* FIX: https://gitlab.com/caosdb/caosdb-crawler/-/issues/30
+
 
 ### Security ###
 
diff --git a/src/caoscrawler/crawl.py b/src/caoscrawler/crawl.py
index 57b2735c8d2ec590822c0a1bf1ebf40cf6208f2c..6187322b902ed9ea5861a945c318c79b018ccf16 100644
--- a/src/caoscrawler/crawl.py
+++ b/src/caoscrawler/crawl.py
@@ -500,7 +500,8 @@ class Crawler(object):
                 return True
         return False
 
-    def create_flat_list(self, ent_list: List[db.Entity], flat: List[db.Entity]):
+    @staticmethod
+    def create_flat_list(ent_list: List[db.Entity], flat: List[db.Entity]):
         """
         Recursively adds all properties contained in entities from ent_list to
         the output list flat. Each element will only be added once to the list.
@@ -516,13 +517,11 @@ class Crawler(object):
                         if isinstance(el, db.Entity):
                             if el not in flat:
                                 flat.append(el)
-                            # TODO: move inside if block?
-                            self.create_flat_list([el], flat)
+                                Crawler.create_flat_list([el], flat)
                 elif isinstance(p.value, db.Entity):
                     if p.value not in flat:
                         flat.append(p.value)
-                    # TODO: move inside if block?
-                    self.create_flat_list([p.value], flat)
+                        Crawler.create_flat_list([p.value], flat)
 
     def has_missing_object_in_references(self, record: db.Record):
         """
@@ -696,7 +695,7 @@ class Crawler(object):
         to_be_updated: List[db.Entity] = []
         flat = list(ent_list)
         # assure all entities are direct members TODO Can this be removed at some point?Check only?
-        self.create_flat_list(ent_list, flat)
+        Crawler.create_flat_list(ent_list, flat)
 
         # TODO: can the following be removed at some point
         for ent in flat:
diff --git a/unittests/test_tool.py b/unittests/test_tool.py
index f08f8061728e2819b70079cabc0a10796154f619..85440fc76ca3dbdec4a88862abbc7d961fee8f5f 100755
--- a/unittests/test_tool.py
+++ b/unittests/test_tool.py
@@ -713,3 +713,9 @@ def test_security_mode(updateCacheMock, upmock, insmock, ident):
     reset_mocks([updateCacheMock, insmock, upmock])
     # restore original ident
     ident._records = deepcopy(records_backup)
+
+
+def test_create_flat_list():
+    a = db.Record()
+    a.add_property(name="a", value=a)
+    Crawler.create_flat_list([a], [])