diff --git a/src/Generator/DefaultArgumentGenerator.php b/src/Generator/DefaultArgumentGenerator.php
index 891c4b77..ef41305a 100644
--- a/src/Generator/DefaultArgumentGenerator.php
+++ b/src/Generator/DefaultArgumentGenerator.php
@@ -88,7 +88,8 @@ trait DefaultArgumentGenerator
                         $code .= 'return ' . $plan->expr . ';' . PHP_EOL;
                     }
                 } else {
-                    $code .= 'return ' . $argInfo->default . ';' . PHP_EOL;
+                    $default = $this->convertRuntimeConstantDefault($type, $argInfo->default);
+                    $code .= 'return ' . $default . ';' . PHP_EOL;
                 }
 
                 $code .= '}' . PHP_EOL . PHP_EOL;
@@ -98,6 +99,28 @@ trait DefaultArgumentGenerator
         return $code;
     }
 
+    /**
+     * Runtime constant lookup returns Variant, but a typed default helper must
+     * return its native C++ type explicitly. Convert the complete expression so
+     * constants nested in expressions are covered as well.
+     */
+    private function convertRuntimeConstantDefault(string $type, string $default): string
+    {
+        if (!str_contains($default, 'php::constant(')) {
+            return $default;
+        }
+
+        return match ($type) {
+            Type::INT => 'php::toInt(' . $default . ')',
+            Type::FLOAT => 'php::toFloat(' . $default . ')',
+            Type::BOOL => 'php::toBool(' . $default . ')',
+            Type::STR => 'php::toString(' . $default . ')',
+            Type::ARRAY => 'php::toArray(' . $default . ')',
+            Type::OBJECT => 'php::toObject(' . $default . ')',
+            default => $default,
+        };
+    }
+
     private function shouldGenerateDefaultArgumentHelper(ArgInfo $argInfo): bool
     {
         if ($argInfo->variadic) {
diff --git a/tests/compiler/const/class-const-default-value-typed.phpt b/tests/compiler/const/class-const-default-value-typed.phpt
new file mode 100644
index 00000000..d9b5d26d
--- /dev/null
+++ b/tests/compiler/const/class-const-default-value-typed.phpt
@@ -0,0 +1,30 @@
+--TEST--
+Typed parameter default value from an unresolvable (external) class constant
+--FILE--
+<?php
+
+class TypedDefault
+{
+    public function run(
+        int $value = \ArrayObject::ARRAY_AS_PROPS,
+        float $floatValue = \ArrayObject::ARRAY_AS_PROPS,
+        string $format = \DateTime::ATOM,
+        int $composite = 1 | \ArrayObject::ARRAY_AS_PROPS,
+        mixed $variant = \ArrayObject::STD_PROP_LIST,
+    )
+    {
+        var_dump($value, $floatValue, $format, $composite, $variant);
+    }
+}
+
+function main()
+{
+    (new TypedDefault)->run();
+}
+?>
+--EXPECT--
+int(2)
+float(2)
+string(13) "Y-m-d\TH:i:sP"
+int(3)
+int(1)