diff --git a/app/code/Magento/Catalog/Model/Category/Link/SaveHandler.php b/app/code/Magento/Catalog/Model/Category/Link/SaveHandler.php
index 29a1ef60a43de..f22c6903a230c 100644
--- a/app/code/Magento/Catalog/Model/Category/Link/SaveHandler.php
+++ b/app/code/Magento/Catalog/Model/Category/Link/SaveHandler.php
@@ -119,7 +119,9 @@ private function mergeCategoryLinks($newCategoryPositions, $oldCategoryPositions
 
             if ($key === false) {
                 $result[] = $newCategoryPosition;
-            } elseif ($oldCategoryPositions[$key]['position'] != $newCategoryPosition['position']) {
+            } elseif (isset($oldCategoryPositions[$key])
+                && $oldCategoryPositions[$key]['position'] != $newCategoryPosition['position']
+            ) {
                 $result[] = $newCategoryPositions[$key];
                 unset($oldCategoryPositions[$key]);
             }
diff --git a/app/code/Magento/Catalog/Test/Unit/Model/Category/Link/SaveHandlerTest.php b/app/code/Magento/Catalog/Test/Unit/Model/Category/Link/SaveHandlerTest.php
index 78db12be56b42..0b85ef38387fa 100644
--- a/app/code/Magento/Catalog/Test/Unit/Model/Category/Link/SaveHandlerTest.php
+++ b/app/code/Magento/Catalog/Test/Unit/Model/Category/Link/SaveHandlerTest.php
@@ -197,6 +197,21 @@ public function getCategoryDataProvider()
                 ],
                 [], //affected category_ids
             ],
+            [
+                [3], //model category_ids
+                [
+                    ['category_id' => 3, 'position' => 20],
+                    ['category_id' => 4, 'position' => 30],
+                ], // dto category links
+                [
+                    ['category_id' => 3, 'position' => 10],
+                ],
+                [
+                    ['category_id' => 3, 'position' => 20],
+                    ['category_id' => 4, 'position' => 30],
+                ],
+                [3, 4], //affected category_ids
+            ],
         ];
     }