diff --git a/rules-tests/TypeDeclarationDocblocks/Rector/ClassMethod/AddReturnDocblockForCommonObjectDenominatorRector/Fixture/with_string_key.php.inc b/rules-tests/TypeDeclarationDocblocks/Rector/ClassMethod/AddReturnDocblockForCommonObjectDenominatorRector/Fixture/with_string_key.php.inc
new file mode 100644
index 00000000000..fc6e7ecd09d
--- /dev/null
+++ b/rules-tests/TypeDeclarationDocblocks/Rector/ClassMethod/AddReturnDocblockForCommonObjectDenominatorRector/Fixture/with_string_key.php.inc
@@ -0,0 +1,42 @@
+<?php
+
+namespace Rector\Tests\TypeDeclarationDocblocks\Rector\ClassMethod\AddReturnDocblockForCommonObjectDenominatorRector\Fixture;
+
+use Rector\Tests\TypeDeclarationDocblocks\Rector\ClassMethod\AddReturnDocblockForCommonObjectDenominatorRector\Source\FirstExtension;
+use Rector\Tests\TypeDeclarationDocblocks\Rector\ClassMethod\AddReturnDocblockForCommonObjectDenominatorRector\Source\SecondExtension;
+
+final class WithStringKey
+{
+    public function getExtensions(): array
+    {
+        return [
+            'a' => new FirstExtension(),
+            'b' => new SecondExtension()
+        ];
+    }
+}
+
+?>
+-----
+<?php
+
+namespace Rector\Tests\TypeDeclarationDocblocks\Rector\ClassMethod\AddReturnDocblockForCommonObjectDenominatorRector\Fixture;
+
+use Rector\Tests\TypeDeclarationDocblocks\Rector\ClassMethod\AddReturnDocblockForCommonObjectDenominatorRector\Source\FirstExtension;
+use Rector\Tests\TypeDeclarationDocblocks\Rector\ClassMethod\AddReturnDocblockForCommonObjectDenominatorRector\Source\SecondExtension;
+
+final class WithStringKey
+{
+    /**
+     * @return array<string, \Rector\Tests\TypeDeclarationDocblocks\Rector\ClassMethod\AddReturnDocblockForCommonObjectDenominatorRector\Source\Contract\ExtensionInterface>
+     */
+    public function getExtensions(): array
+    {
+        return [
+            'a' => new FirstExtension(),
+            'b' => new SecondExtension()
+        ];
+    }
+}
+
+?>
diff --git a/rules/TypeDeclarationDocblocks/Rector/ClassMethod/AddReturnDocblockForCommonObjectDenominatorRector.php b/rules/TypeDeclarationDocblocks/Rector/ClassMethod/AddReturnDocblockForCommonObjectDenominatorRector.php
index b699c423dbc..b12e0b160d4 100644
--- a/rules/TypeDeclarationDocblocks/Rector/ClassMethod/AddReturnDocblockForCommonObjectDenominatorRector.php
+++ b/rules/TypeDeclarationDocblocks/Rector/ClassMethod/AddReturnDocblockForCommonObjectDenominatorRector.php
@@ -12,7 +12,11 @@
 use PHPStan\Reflection\ReflectionProvider;
 use PHPStan\Type\ArrayType;
 use PHPStan\Type\Constant\ConstantArrayType;
+use PHPStan\Type\IntegerType;
 use PHPStan\Type\MixedType;
+use PHPStan\Type\StringType;
+use PHPStan\Type\Type;
+use PHPStan\Type\UnionType;
 use Rector\BetterPhpDocParser\PhpDocInfo\PhpDocInfoFactory;
 use Rector\BetterPhpDocParser\PhpDocManipulator\PhpDocTypeChanger;
 use Rector\Rector\AbstractRector;
@@ -30,7 +34,7 @@ public function __construct(
         private readonly PhpDocInfoFactory $phpDocInfoFactory,
         private readonly ReturnNodeFinder $returnNodeFinder,
         private readonly ReflectionProvider $reflectionProvider,
-        private readonly PhpDocTypeChanger $phpDocTypeChanger,
+        private readonly PhpDocTypeChanger $phpDocTypeChanger
     ) {
     }
 
@@ -167,7 +171,10 @@ public function refactor(Node $node): ?Node
             return null;
         }
 
-        $objectTypeArrayType = new ArrayType(new MixedType(), new FullyQualifiedObjectType($firstSharedType));
+        $objectTypeArrayType = new ArrayType(
+            $this->resolveKeyType($returnedType),
+            new FullyQualifiedObjectType($firstSharedType)
+        );
         $hasChanged = $this->phpDocTypeChanger->changeReturnType($node, $phpDocInfo, $objectTypeArrayType);
         if (! $hasChanged) {
             return null;
@@ -176,6 +183,36 @@ public function refactor(Node $node): ?Node
         return $node;
     }
 
+    /**
+     * @return UnionType|IntegerType|StringType|MixedType
+     */
+    private function resolveKeyType(ConstantArrayType $constantArrayType): Type
+    {
+        $keyType = $constantArrayType->getKeyType();
+
+        if ($keyType instanceof UnionType) {
+            $types = [];
+            foreach ($keyType->getTypes() as $type) {
+                if ($type->isString()->yes()) {
+                    $types[] = new StringType();
+                } elseif ($type->isInteger()->yes()) {
+                    $types[] = new IntegerType();
+                } else {
+                    return new MixedType();
+                }
+            }
+
+            $uniqueKeyTypes = array_unique($types, SORT_REGULAR);
+            if (count($uniqueKeyTypes) === 1) {
+                return $uniqueKeyTypes[0];
+            }
+
+            return new UnionType($uniqueKeyTypes);
+        }
+
+        return new MixedType();
+    }
+
     /**
      * @return string[]
      */