diff --git a/src/codegen.inc.php b/src/codegen.inc.php
index 59b345a..c5d7e5a 100644
--- a/src/codegen.inc.php
+++ b/src/codegen.inc.php
@@ -209,7 +209,7 @@ function data2value($name, \mtgType $type, $buf, $prefix = '', $tokens = array()
     if(array_key_exists('virtual', $tokens))
     {
       $str .= $cond_indent."\$vclass__ = AutogenBundle::getClassName(\metagen_php\\val_uint32(\metagen_php\array_extract_val(\$tmp_sub_arr__, \$assoc, '\$id', {$type->getClassId()})));\n";
-      $str .= $cond_indent."if(!is_subclass_of(\$vclass__, '{$type->getName()}')) throw new Exception(\$vclass__ . ' is not subclass of {$type->getName()}');\n";
+      $str .= $cond_indent."if(!is_subclass_of(\$vclass__, '{$type->getName()}')) throw new Exception(\"'\$vclass__' is not subclass of '{$type->getName()}'\");\n";
       $str .= $cond_indent."{$pname} = new \$vclass__(\$tmp_sub_arr__, \$assoc);\n";
     }
     else