diff --git a/src/lib/Persistence/Cache/ContentHandler.php b/src/lib/Persistence/Cache/ContentHandler.php
index a54e6bb293..68d8027f02 100644
--- a/src/lib/Persistence/Cache/ContentHandler.php
+++ b/src/lib/Persistence/Cache/ContentHandler.php
@@ -445,6 +445,10 @@ public function addRelation(RelationCreateStruct $relation)
                 self::CONTENT_IDENTIFIER,
                 [$relation->destinationContentId]
             ),
+            $this->cacheIdentifierGenerator->generateTag(
+                self::CONTENT_IDENTIFIER,
+                [$relation->sourceContentId]
+            ),
         ]);
 
         return $this->persistenceHandler->contentHandler()->addRelation($relation);
diff --git a/tests/lib/Persistence/Cache/ContentHandlerTest.php b/tests/lib/Persistence/Cache/ContentHandlerTest.php
index 38ccfcae05..7ce7d7bd6a 100644
--- a/tests/lib/Persistence/Cache/ContentHandlerTest.php
+++ b/tests/lib/Persistence/Cache/ContentHandlerTest.php
@@ -51,7 +51,7 @@ public function providerForUnCachedMethods(): array
             ['updateContent', [2, 1, new UpdateStruct()], [['content_version', [2, 1], false]], null, ['c-2-v-1']],
             //['deleteContent', [2]], own tests for relations complexity
             ['deleteVersion', [2, 1], [['content_version', [2, 1], false]], null, ['c-2-v-1']],
-            ['addRelation', [new RelationCreateStruct(['destinationContentId' => 2])], [['content', [2], false]], null, ['c-2']],
+            ['addRelation', [new RelationCreateStruct(['destinationContentId' => 2, 'sourceContentId' => 4])], [['content', [2], false], ['content', [4], false]], null, ['c-2', 'c-4']],
             ['removeRelation', [66, APIRelation::COMMON, 2], [['content', [2], false], ['relation', [66], false]], null, ['c-2', 're-66']],
             ['loadRelations', [2, 1, 3]],
             ['loadReverseRelations', [2, 3]],