diff --git a/CHANGELOG.md b/CHANGELOG.md
index c59d172f..937f464a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,7 @@ Features
 
  - Faster record type constructors
  - During compilation, validate the number of arguments passed to local function calls.
+ - Added `-use-unsafe-prims` compiler option to allow generating faster code at the expense of runtime checks.
 
 Bug Fixes
 
diff --git a/include/cyclone/runtime.h b/include/cyclone/runtime.h
index 2bdb4acc..e8752f55 100644
--- a/include/cyclone/runtime.h
+++ b/include/cyclone/runtime.h
@@ -487,7 +487,7 @@ object Cyc_is_immutable(object obj);
 object Cyc_vector_length(void *data, object v);
 object Cyc_vector_ref(void *d, object v, object k);
 #define Cyc_vector_ref_unsafe(d, v, k) \
-  ((vector) v)->elements[unbox_number(k)]
+  ((vector) v)->elements[obj_obj2int(k)]
 object Cyc_vector_set(void *d, object v, object k, object obj);
 object Cyc_make_vector(void *data, object cont, int argc, object len, ...);
 /**@}*/