diff --git a/rules-tests/TypeDeclarationDocblocks/Rector/Class_/ClassMethodArrayDocblockParamFromLocalCallsRector/Fixture/skip_heterogeneous_nested_array_key.php.inc b/rules-tests/TypeDeclarationDocblocks/Rector/Class_/ClassMethodArrayDocblockParamFromLocalCallsRector/Fixture/skip_heterogeneous_nested_array_key.php.inc
new file mode 100644
index 00000000000..fa57efe6e77
--- /dev/null
+++ b/rules-tests/TypeDeclarationDocblocks/Rector/Class_/ClassMethodArrayDocblockParamFromLocalCallsRector/Fixture/skip_heterogeneous_nested_array_key.php.inc
@@ -0,0 +1,21 @@
+<?php
+
+namespace Rector\Tests\TypeDeclarationDocblocks\Rector\Class_\ClassMethodArrayDocblockParamFromLocalCallsRector\Fixture;
+
+class SkipHeterogeneousNestedArrayKey
+{
+    public function one()
+    {
+        return $this->sink([["x" => 1], "s"]);
+    }
+
+    public function two()
+    {
+        return $this->sink([[["d" => 1]]]);
+    }
+
+    protected function sink(array $data)
+    {
+        return $data;
+    }
+}
diff --git a/rules/Privatization/TypeManipulator/TypeNormalizer.php b/rules/Privatization/TypeManipulator/TypeNormalizer.php
index 11ce83a5cc5..8594031162a 100644
--- a/rules/Privatization/TypeManipulator/TypeNormalizer.php
+++ b/rules/Privatization/TypeManipulator/TypeNormalizer.php
@@ -196,10 +196,14 @@ private function narrowToAlwaysKnownArrayType(UnionType $unionType): ?ArrayType
             return null;
         }
 
-        $arrayUniqueKeyType = $this->arrayTypeLeastCommonDenominatorResolver->sharedArrayStructure(
+        $sharedArrayStructure = $this->arrayTypeLeastCommonDenominatorResolver->sharedArrayStructure(
             ...$unionType->getTypes()
         );
-        return new ArrayType($arrayUniqueKeyType, new MixedType());
+        if (! $sharedArrayStructure instanceof ArrayType) {
+            return null;
+        }
+
+        return $sharedArrayStructure;
     }
 
     /**