diff --git a/src/Psalm/Internal/PhpVisitor/Reflector/FunctionLikeNodeScanner.php b/src/Psalm/Internal/PhpVisitor/Reflector/FunctionLikeNodeScanner.php
index fa4d4a36c46..4d85c3c8413 100644
--- a/src/Psalm/Internal/PhpVisitor/Reflector/FunctionLikeNodeScanner.php
+++ b/src/Psalm/Internal/PhpVisitor/Reflector/FunctionLikeNodeScanner.php
@@ -631,12 +631,13 @@ public function start(PhpParser\Node\FunctionLike $stmt, bool $fake_method = fal
                 $property_storage->location = $param_storage->location;
                 $property_storage->stmt_location = new CodeLocation($this->file_scanner, $param);
                 $property_storage->has_default = (bool)$param->default;
+                $property_storage->readonly = (bool)($param->flags & PhpParser\Node\Stmt\Class_::MODIFIER_READONLY);
                 $param_storage->promoted_property = true;
                 $property_storage->is_promoted = true;
 
                 $property_id = $fq_classlike_name . '::$' . $param_storage->name;
 
-                switch ($param->flags) {
+                switch ($param->flags & \PhpParser\Node\Stmt\Class_::VISIBILITY_MODIFIER_MASK) {
                     case \PhpParser\Node\Stmt\Class_::MODIFIER_PUBLIC:
                         $property_storage->visibility = ClassLikeAnalyzer::VISIBILITY_PUBLIC;
                         $classlike_storage->inheritable_property_ids[$param_storage->name] = $property_id;
diff --git a/tests/ReadonlyPropertyTest.php b/tests/ReadonlyPropertyTest.php
index 7f3a0f131c9..8bec3192352 100644
--- a/tests/ReadonlyPropertyTest.php
+++ b/tests/ReadonlyPropertyTest.php
@@ -243,6 +243,34 @@ class A {
                 false,
                 '8.1',
             ],
+            'readonlyPromotedPropertyAssignOperator' => [
+                '<?php
+                    class A {
+                        public function __construct(public readonly string $bar) {
+                        }
+                    }
+
+                    $a = new A("hello");
+                    $a->bar = "goodbye";',
+                'error_message' => 'InaccessibleProperty - src' . DIRECTORY_SEPARATOR . 'somefile.php:8:21',
+                [],
+                false,
+                '8.1',
+            ],
+            'readonlyPromotedPropertyAccess' => [
+                '<?php
+                    class A {
+                        public function __construct(private readonly string $bar) {
+                        }
+                    }
+
+                    $a = new A("hello");
+                    $b = $a->bar;',
+                'error_message' => 'InaccessibleProperty - src' . DIRECTORY_SEPARATOR . 'somefile.php:8:26',
+                [],
+                false,
+                '8.1',
+            ],
         ];
     }
 }