diff --git a/rules-tests/Php80/Rector/Class_/ClassPropertyAssignToConstructorPromotionRector/Fixture/skip_untyped_parent_property.php.inc b/rules-tests/Php80/Rector/Class_/ClassPropertyAssignToConstructorPromotionRector/Fixture/skip_untyped_parent_property.php.inc
new file mode 100644
index 00000000000..4ca0eec8ddc
--- /dev/null
+++ b/rules-tests/Php80/Rector/Class_/ClassPropertyAssignToConstructorPromotionRector/Fixture/skip_untyped_parent_property.php.inc
@@ -0,0 +1,19 @@
+<?php
+
+namespace Rector\Tests\Php80\Rector\Class_\ClassPropertyAssignToConstructorPromotionRector\Fixture;
+
+use Rector\Tests\Php80\Rector\Class_\ClassPropertyAssignToConstructorPromotionRector\Source\SomeCacheProvider;
+use Rector\Tests\Php80\Rector\Class_\ClassPropertyAssignToConstructorPromotionRector\Source\UntypedPropertyParent;
+
+final class SkipUntypedParentProperty extends UntypedPropertyParent
+{
+    /**
+     * @var SomeCacheProvider|null
+     */
+    protected $model;
+
+    public function __construct(SomeCacheProvider $model)
+    {
+        $this->model = $model;
+    }
+}
diff --git a/rules-tests/Php80/Rector/Class_/ClassPropertyAssignToConstructorPromotionRector/Source/UntypedPropertyParent.php b/rules-tests/Php80/Rector/Class_/ClassPropertyAssignToConstructorPromotionRector/Source/UntypedPropertyParent.php
new file mode 100644
index 00000000000..f5e532c00f5
--- /dev/null
+++ b/rules-tests/Php80/Rector/Class_/ClassPropertyAssignToConstructorPromotionRector/Source/UntypedPropertyParent.php
@@ -0,0 +1,13 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Rector\Tests\Php80\Rector\Class_\ClassPropertyAssignToConstructorPromotionRector\Source;
+
+abstract class UntypedPropertyParent
+{
+    /**
+     * @var SomeCacheProvider|null
+     */
+    protected $model;
+}
diff --git a/rules/Php80/Rector/Class_/ClassPropertyAssignToConstructorPromotionRector.php b/rules/Php80/Rector/Class_/ClassPropertyAssignToConstructorPromotionRector.php
index 98a2ca0e1dd..9aab5246b6d 100644
--- a/rules/Php80/Rector/Class_/ClassPropertyAssignToConstructorPromotionRector.php
+++ b/rules/Php80/Rector/Class_/ClassPropertyAssignToConstructorPromotionRector.php
@@ -227,6 +227,10 @@ public function refactor(Node $node): ?Node
                 continue;
             }
 
+            if ($this->shouldSkipUntypedParentProperty($classReflection, $propertyName)) {
+                continue;
+            }
+
             $hasChanged = true;
 
             // remove property from class
@@ -347,6 +351,25 @@ private function processUnionType(Property $property, Param $param): void
         $param->type = $this->staticTypeMapper->mapPHPStanTypeToPhpParserNode($paramType, TypeKind::PARAM);
     }
 
+    /**
+     * A parent property declared without a native type cannot be typed by a child. Promotion moves the param
+     * type onto the property, so promoting such a property makes the class fatal:
+     * "Type of Child::$property must not be defined (as in class Parent)".
+     */
+    private function shouldSkipUntypedParentProperty(ClassReflection $classReflection, string $propertyName): bool
+    {
+        foreach ($classReflection->getParents() as $parentClassReflection) {
+            if (! $parentClassReflection->hasNativeProperty($propertyName)) {
+                continue;
+            }
+
+            return ! $parentClassReflection->getNativeProperty($propertyName)
+                ->hasNativeType();
+        }
+
+        return false;
+    }
+
     private function shouldSkipParam(Param $param): bool
     {
         if ($param->variadic) {