diff --git a/vm/capi/string.cpp b/vm/capi/string.cpp
index c4f499b..b07fcb9 100644
--- a/vm/capi/string.cpp
+++ b/vm/capi/string.cpp
@@ -367,9 +367,9 @@ extern "C" {
     NativeMethodEnvironment* env = NativeMethodEnvironment::get();
 
     String* string = capi_get_string(env, self);
-    if(string->size() > len) {
+    if(string->data()->size() > len) {
       string->byte_address()[len] = 0;
-      string->num_bytes(env->state(), Fixnum::from(len));
     }
+    string->num_bytes(env->state(), Fixnum::from(len));
   }
 }