diff --git a/packages/NodeTypeResolver/src/PhpDoc/NodeAnalyzer/DocBlockManipulator.php b/packages/NodeTypeResolver/src/PhpDoc/NodeAnalyzer/DocBlockManipulator.php
index 653dbcddab7..f418cf6795f 100644
--- a/packages/NodeTypeResolver/src/PhpDoc/NodeAnalyzer/DocBlockManipulator.php
+++ b/packages/NodeTypeResolver/src/PhpDoc/NodeAnalyzer/DocBlockManipulator.php
@@ -16,6 +16,7 @@ use PHPStan\PhpDocParser\Ast\PhpDoc\PhpDocChildNode;
 use PHPStan\PhpDocParser\Ast\PhpDoc\PhpDocNode;
 use PHPStan\PhpDocParser\Ast\PhpDoc\PhpDocTagNode;
 use PHPStan\PhpDocParser\Ast\PhpDoc\PhpDocTagValueNode;
+use PHPStan\PhpDocParser\Ast\PhpDoc\ReturnTagValueNode;
 use PHPStan\PhpDocParser\Ast\PhpDoc\VarTagValueNode;
 use PHPStan\PhpDocParser\Ast\Type\IdentifierTypeNode;
 use PHPStan\Type\ArrayType;
@@ -288,7 +289,20 @@ final class DocBlockManipulator
             return;
         }
 
-        $this->removeTagFromNode($node, 'return');
+        if ($node->getDocComment()) {
+            $phpDocInfo = $this->createPhpDocInfoFromNode($node);
+            $returnTagValueNode = $phpDocInfo->getByType(ReturnTagValueNode::class);
+
+            // overide existing type
+            if ($returnTagValueNode) {
+                $newPHPStanPhpDocType = $this->staticTypeMapper->mapPHPStanTypeToPHPStanPhpDocTypeNode($newType);
+                $returnTagValueNode->type = $newPHPStanPhpDocType;
+
+                $this->updateNodeWithPhpDocInfo($node, $phpDocInfo);
+                return;
+            }
+        }
+
         $this->addTypeSpecificTag($node, 'return', $newType);
     }
 
diff --git a/packages/NodeTypeResolver/src/StaticTypeMapper.php b/packages/NodeTypeResolver/src/StaticTypeMapper.php
index dec4cac3634..4be091d0076 100644
--- a/packages/NodeTypeResolver/src/StaticTypeMapper.php
+++ b/packages/NodeTypeResolver/src/StaticTypeMapper.php
@@ -101,6 +101,8 @@ final class StaticTypeMapper
                 $unionTypesNodes[] = $this->mapPHPStanTypeToPHPStanPhpDocTypeNode($unionedType);
             }
 
+            $unionTypesNodes = array_unique($unionTypesNodes);
+
             return new AttributeAwareUnionTypeNode($unionTypesNodes);
         }
 
@@ -129,6 +131,10 @@ final class StaticTypeMapper
             return new IdentifierTypeNode('\\' . $phpStanType->getClassName());
         }
 
+        if ($phpStanType instanceof NullType) {
+            return new IdentifierTypeNode('null');
+        }
+
         throw new NotImplementedException(__METHOD__ . ' for ' . get_class($phpStanType));
     }
 
diff --git a/packages/TypeDeclaration/tests/Rector/ClassMethod/AddArrayReturnDocTypeRector/Fixture/with_comment.php.inc b/packages/TypeDeclaration/tests/Rector/ClassMethod/AddArrayReturnDocTypeRector/Fixture/with_comment.php.inc
new file mode 100644
index 00000000000..03aeaaa781f
--- /dev/null
+++ b/packages/TypeDeclaration/tests/Rector/ClassMethod/AddArrayReturnDocTypeRector/Fixture/with_comment.php.inc
@@ -0,0 +1,43 @@
+<?php
+
+namespace Rector\TypeDeclaration\Tests\Rector\ClassMethod\AddArrayReturnDocTypeRector\Fixture;
+
+class WithComment
+{
+    /**
+     * @var int[]
+     */
+    private $values;
+
+    /**
+     * @return mixed[] some integer values
+     */
+    public function getValues()
+    {
+        return $this->values;
+    }
+}
+
+?>
+-----
+<?php
+
+namespace Rector\TypeDeclaration\Tests\Rector\ClassMethod\AddArrayReturnDocTypeRector\Fixture;
+
+class WithComment
+{
+    /**
+     * @var int[]
+     */
+    private $values;
+
+    /**
+     * @return int[] some integer values
+     */
+    public function getValues()
+    {
+        return $this->values;
+    }
+}
+
+?>