diff --git a/testdata/integration/callable.go b/testdata/integration/callable.go
index 009c7221..731ad5fa 100644
--- a/testdata/integration/callable.go
+++ b/testdata/integration/callable.go
@@ -58,7 +58,7 @@ func (p *Processor) Transform(input *C.zend_string, callback *C.zval) unsafe.Poi
 
 	resultStr, ok := callResult.(string)
 	if !ok {
-		return unsafe.Pointer(input)
+		return frankenphp.PHPString(input, false)
 	}
 
 	return frankenphp.PHPString(resultStr, false)