diff --git a/runtime/src/juvix/api.h b/runtime/src/juvix/api.h
index 1a1bab2e0c..3857472cc0 100644
--- a/runtime/src/juvix/api.h
+++ b/runtime/src/juvix/api.h
@@ -112,7 +112,7 @@
         error_exit();      \
     } while (0)
 
-#define JUVIX_ARGS_NUM(var, val) (var = get_closure_largs(val))
+#define JUVIX_ARGS_NUM(var, val) (var = make_smallint(get_closure_largs(val)))
 
 #define JUVIX_ALLOC_INT(var, val) (var = make_smallint(val))
 // ALLOC_CONSTR_BOXED(var, uid, nargs)