diff --git a/news/89.bugfix b/news/89.bugfix
new file mode 100644
index 0000000..6a24dd6
--- /dev/null
+++ b/news/89.bugfix
@@ -0,0 +1,3 @@
+- Update relations on Check-In WorkingCopy, by trigger an ObjectModifiedEvent event
+- black and flake8 formatting
+[2silver]
\ No newline at end of file
diff --git a/plone/app/iterate/dexterity/policy.py b/plone/app/iterate/dexterity/policy.py
index f88c69c..e90911c 100644
--- a/plone/app/iterate/dexterity/policy.py
+++ b/plone/app/iterate/dexterity/policy.py
@@ -13,6 +13,7 @@
 from zope.component import adapter
 from zope.component import queryAdapter
 from zope.event import notify
+from zope.lifecycleevent import ObjectModifiedEvent
 
 
 @adapter(IDexterityIterateAware)
@@ -34,6 +35,10 @@ def checkin(self, checkin_message):
         new_baseline = copier.merge()
         # don't need to unlock the lock disappears with old baseline deletion
         notify(AfterCheckinEvent(new_baseline, checkin_message))
+
+        # update our new_baseline, ex. for all References ( and BackReferences)
+        notify(ObjectModifiedEvent(new_baseline))
+
         return new_baseline
 
     def _get_relation_to_baseline(self):
diff --git a/plone/app/iterate/tests/test_iterate.py b/plone/app/iterate/tests/test_iterate.py
index 8fcf288..9739f6a 100644
--- a/plone/app/iterate/tests/test_iterate.py
+++ b/plone/app/iterate/tests/test_iterate.py
@@ -142,9 +142,13 @@ def test_folderContents(self):
         version of the folder.  UIDs of contained content are also
         preserved."""
         container = self.portal.docs
-        folder = container[container.invokeFactory(type_name="Folder", id="foo-folder")]
+        folder = container[
+            container.invokeFactory(type_name="Folder", id="foo-folder")
+        ]
         existing_doc = folder[
-            folder.invokeFactory(type_name="Document", id="existing-folder-item")
+            folder.invokeFactory(
+                type_name="Document", id="existing-folder-item"
+            )
         ]
         existing_doc_uid = existing_doc.UID()
 
@@ -152,7 +156,9 @@ def test_folderContents(self):
         wc = ICheckinCheckoutPolicy(folder).checkout(container)
         new_doc = wc[
             wc.invokeFactory(
-                type_name="Document", id="new-folder-item", text="new folder item text"
+                type_name="Document",
+                id="new-folder-item",
+                text="new folder item text",
             )
         ]
         new_doc_uid = new_doc.UID()
@@ -161,10 +167,14 @@ def test_folderContents(self):
         catalog = getToolByName(self.portal, "portal_catalog")
 
         self.assertTrue("existing-folder-item" in new_folder)
-        self.assertEqual(new_folder["existing-folder-item"].UID(), existing_doc_uid)
+        self.assertEqual(
+            new_folder["existing-folder-item"].UID(), existing_doc_uid
+        )
         self.assertTrue("new-folder-item" in new_folder)
         self.assertEqual(new_folder["new-folder-item"].UID(), new_doc_uid)
-        brains = catalog(path="/".join(new_folder["new-folder-item"].getPhysicalPath()))
+        brains = catalog(
+            path="/".join(new_folder["new-folder-item"].getPhysicalPath())
+        )
         self.assertTrue(brains)
         self.assertTrue(
             "new folder item text" in new_folder["new-folder-item"].getText()
@@ -281,3 +291,51 @@ def test_relationship_deleted_on_cancel_checkout(self):
         rels = list(catalog.findRelations({"from_id": obj_id}))
 
         self.assertEqual(len(rels), 0)
+
+    def test_baseline_relations_updated_on_checkin(self):
+        # Ensure that relations between the baseline and
+        # and other objects are up-to-date on checkin
+        from zope.event import notify
+        from zope.lifecycleevent import ObjectModifiedEvent
+        from z3c.relationfield import RelationValue
+
+        folder = self.portal.docs
+        baseline = folder.doc1
+        target = folder.doc2
+
+        intids = component.getUtility(IIntIds)
+        catalog = component.getUtility(ICatalog)
+
+        target_id = intids.getId(target)
+        target_rel = [RelationValue(target_id)]
+
+        # Test, if nothing is present in the relation catalog
+        rels = list(catalog.findRelations({"to_id": target_id}))
+        self.assertEqual(len(rels), 0)
+
+        # set relatedItems on baseline
+        baseline.relatedItems = target_rel
+        notify(ObjectModifiedEvent(baseline))
+
+        # Test, if relation is present in the relation catalog
+        rels = list(catalog.findRelations({"to_id": target_id}))
+        self.assertEqual(len(rels), 1)
+
+        # make a workingcopy from baseline
+        wc = ICheckinCheckoutPolicy(baseline).checkout(folder)
+
+        # remove relations on wc
+        wc.relatedItems = []
+        notify(ObjectModifiedEvent(wc))
+
+        # baseline -> target relation should be still there, we are on wc
+        rels = list(catalog.findRelations({"to_id": target_id}))
+        self.assertEqual(len(rels), 1)
+
+        # baseline -> target relation should be empty now
+        # because we replaced our baseline with our wc (with empty relations)
+        baseline = ICheckinCheckoutPolicy(wc).checkin("updated")
+        rels = list(catalog.findRelations({"to_id": target_id}))
+
+        # new baseline's relatedItems should be empty
+        self.assertEqual(len(rels), 0)