diff --git a/src/Parser/PropertyAccessTrait.php b/src/Parser/PropertyAccessTrait.php
index c0b7931e..1c177c9a 100644
--- a/src/Parser/PropertyAccessTrait.php
+++ b/src/Parser/PropertyAccessTrait.php
@@ -870,14 +870,16 @@ protected function wrapObjectPropertyAssignTypeCheck(NodeAbstract $left, Expr $r
             return $rightExpr;
         }
 
-        if ($rightType !== Type::VAR && $this->canAssignStaticTypeToObjectProperty($def, $rightType)) {
+        $rightClass = $this->detectClassOfExpr($right);
+        // "object" matches any class by storage type alone; keep the runtime is-a check.
+        $unknownObjectIntoTypedProperty = $rightType === Type::OBJECT && $def->class !== '' && $rightClass === '';
+        if ($rightType !== Type::VAR && $this->canAssignStaticTypeToObjectProperty($def, $rightType) && !$unknownObjectIntoTypedProperty) {
             return $rightExpr;
         }
         if ($rightType === Type::VAR && ($helper = $this->getFixedPropertyTypeCheckHelper($def)) !== null) {
             return $helper . '(' . $rightExpr . ', ' . $this->genCharPtr($this->getObjectPropertyTypeCheckDisplayName($left), true) . ')';
         }
 
-        $rightClass = $this->detectClassOfExpr($right);
         if ($rightClass !== '' && $compositeRelation === null) {
             return $rightExpr;
         }
diff --git a/tests/compiler/object_property/object-param-unknown-class-assign.phpt b/tests/compiler/object_property/object-param-unknown-class-assign.phpt
new file mode 100644
index 00000000..a2b82060
--- /dev/null
+++ b/tests/compiler/object_property/object-param-unknown-class-assign.phpt
@@ -0,0 +1,94 @@
+--TEST--
+object values with a statically unknown class keep the typed property is-a check
+--FILE--
+<?php
+class ParamTargetExpected
+{
+    public function value(): string
+    {
+        return 'expected';
+    }
+}
+
+class ParamTargetChild extends ParamTargetExpected
+{
+}
+
+class ParamTargetOther
+{
+}
+
+class ParamHolder
+{
+    public ParamTargetExpected $p;
+    public ?ParamTargetExpected $nullable;
+    public object $generic;
+}
+
+function assignObject(object $value, ParamHolder $holder): void
+{
+    $holder->p = $value;
+}
+
+function assignNullableObject(object $value, ParamHolder $holder): void
+{
+    $holder->nullable = $value;
+}
+
+function assignGenericObject(object $value, ParamHolder $holder): void
+{
+    $holder->generic = $value;
+}
+
+function main()
+{
+    $holder = new ParamHolder();
+
+    try {
+        assignObject(new ParamTargetExpected(), $holder);
+        echo "valid assignment accepted\n";
+        var_dump($holder->p->value());
+    } catch (Throwable $error) {
+        echo $error::class, "\n";
+    }
+
+    try {
+        assignObject(new ParamTargetChild(), $holder);
+        echo "subclass assignment accepted\n";
+        var_dump($holder->p->value());
+    } catch (Throwable $error) {
+        echo $error::class, "\n";
+    }
+
+    try {
+        assignObject(new ParamTargetOther(), $holder);
+        echo "invalid assignment accepted\n";
+    } catch (Throwable $error) {
+        echo $error::class, "\n";
+    }
+
+    try {
+        assignNullableObject(new ParamTargetOther(), $holder);
+        echo "invalid nullable assignment accepted\n";
+    } catch (Throwable $error) {
+        echo $error::class, "\n";
+    }
+
+    try {
+        assignGenericObject(new ParamTargetOther(), $holder);
+        echo "generic object assignment accepted\n";
+        var_dump($holder->generic::class);
+    } catch (Throwable $error) {
+        echo $error::class, "\n";
+    }
+}
+?>
+--EXPECT--
+valid assignment accepted
+string(8) "expected"
+subclass assignment accepted
+string(8) "expected"
+TypeError
+TypeError
+generic object assignment accepted
+string(16) "ParamTargetOther"