diff --git a/rules-tests/TypedCollections/Rector/Class_/CompleteReturnDocblockFromToManyRector/Fixture/OneToMany/skip_with_string_key.php.inc b/rules-tests/TypedCollections/Rector/Class_/CompleteReturnDocblockFromToManyRector/Fixture/OneToMany/skip_with_string_key.php.inc
new file mode 100644
index 00000000..739ba100
--- /dev/null
+++ b/rules-tests/TypedCollections/Rector/Class_/CompleteReturnDocblockFromToManyRector/Fixture/OneToMany/skip_with_string_key.php.inc
@@ -0,0 +1,25 @@
+<?php
+
+namespace Rector\Doctrine\Tests\TypedCollections\Rector\Class_\CompleteReturnDocblockFromToManyRector\Fixture\OneToMany;
+
+ use Doctrine\ORM\Mapping as ORM;
+
+ /**
+  * @ORM\Entity
+  */
+ final class Trainer
+ {
+     /**
+      * @ORM\OneToMany(targetEntity=Training::class, indexBy=someField)
+      * @var \Doctrine\Common\Collections\Collection<string, Training>
+      */
+     private $trainings;
+
+     /**
+      * @return \Doctrine\Common\Collections\Collection<string, Training>
+      */
+     public function getTrainings()
+     {
+         return $this->trainings;
+     }
+ }
\ No newline at end of file
diff --git a/rules/TypedCollections/DocBlockProcessor/UnionCollectionTagValueNodeNarrower.php b/rules/TypedCollections/DocBlockProcessor/UnionCollectionTagValueNodeNarrower.php
index f1329157..bc5c8287 100644
--- a/rules/TypedCollections/DocBlockProcessor/UnionCollectionTagValueNodeNarrower.php
+++ b/rules/TypedCollections/DocBlockProcessor/UnionCollectionTagValueNodeNarrower.php
@@ -220,7 +220,8 @@ private function isCollectionIdentifierTypeNode(TypeNode $typeNode): bool
 
         return in_array(
             $typeNode->name,
-            [DoctrineClass::COLLECTION, DoctrineClass::ARRAY_COLLECTION, 'Collection', 'ArrayCollection']
+            [DoctrineClass::COLLECTION, DoctrineClass::ARRAY_COLLECTION, 'Collection', 'ArrayCollection'],
+            true
         );
     }
 }
diff --git a/rules/TypedCollections/Rector/Class_/CompleteReturnDocblockFromToManyRector.php b/rules/TypedCollections/Rector/Class_/CompleteReturnDocblockFromToManyRector.php
index f7056927..7c4edf2c 100644
--- a/rules/TypedCollections/Rector/Class_/CompleteReturnDocblockFromToManyRector.php
+++ b/rules/TypedCollections/Rector/Class_/CompleteReturnDocblockFromToManyRector.php
@@ -7,6 +7,7 @@
 use PhpParser\Node;
 use PhpParser\Node\Stmt\Class_;
 use PhpParser\Node\Stmt\Property;
+use PHPStan\Type\Generic\GenericObjectType;
 use Rector\BetterPhpDocParser\PhpDocInfo\PhpDocInfoFactory;
 use Rector\BetterPhpDocParser\PhpDocManipulator\PhpDocTypeChanger;
 use Rector\Doctrine\NodeAnalyzer\MethodUniqueReturnedPropertyResolver;
@@ -134,6 +135,12 @@ public function refactor(Node $node): ?Node
                 $this->collectionTypeResolver->hasIndexBy($property),
                 $property
             );
+
+            $returnType = $phpDocInfo->getReturnType();
+            if ($returnType instanceof GenericObjectType) {
+                continue;
+            }
+
             $this->phpDocTypeChanger->changeReturnType($classMethod, $phpDocInfo, $newVarType);
             $hasChanged = true;
         }