diff --git a/include/picrin/value.h b/include/picrin/value.h
index 97c05c6f..dc8c6297 100644
--- a/include/picrin/value.h
+++ b/include/picrin/value.h
@@ -13,7 +13,7 @@ extern "C" {
  * pic_sym is just an alias to unsigned int.
  */
 
-typedef int pic_sym;
+typedef unsigned int pic_sym;
 
 /**
  * `undef` values never seen from user-end: that is,