diff --git a/include/cyclone/runtime.h b/include/cyclone/runtime.h
index 2d851eed..06793f1a 100644
--- a/include/cyclone/runtime.h
+++ b/include/cyclone/runtime.h
@@ -489,6 +489,7 @@ object Cyc_vector_ref(void *d, object v, object k);
 #define Cyc_vector_ref_unsafe(d, v, k) \
   ((vector) v)->elements[obj_obj2int(k)]
 object Cyc_vector_set(void *d, object v, object k, object obj);
+object Cyc_vector_set_unsafe(void *d, object v, object k, object obj);
 object Cyc_make_vector(void *data, object cont, int argc, object len, ...);
 /**@}*/
 
diff --git a/runtime.c b/runtime.c
index fd6ddaee..cea73af4 100644
--- a/runtime.c
+++ b/runtime.c
@@ -1939,6 +1939,15 @@ object Cyc_vector_set(void *data, object v, object k, object obj)
   return v;
 }
 
+object Cyc_vector_set_unsafe(void *data, object v, object k, object obj)
+{
+  int idx = unbox_number(k);
+  gc_mut_update((gc_thread_data *) data, ((vector) v)->elements[idx], obj);
+  ((vector) v)->elements[idx] = obj;
+  add_mutation(data, v, idx, obj);
+  return v;
+}
+
 object Cyc_vector_ref(void *data, object v, object k)
 {
   int idx;
diff --git a/scheme/cyclone/primitives.sld b/scheme/cyclone/primitives.sld
index 3a8facdf..480dea15 100644
--- a/scheme/cyclone/primitives.sld
+++ b/scheme/cyclone/primitives.sld
@@ -629,7 +629,10 @@
           (if emit-unsafe
               "Cyc_vector_ref_unsafe"
               "Cyc_vector_ref"))
-         ((eq? p 'vector-set!)   "Cyc_vector_set")
+         ((eq? p 'vector-set!)  
+          (if emit-unsafe
+              "Cyc_vector_set_unsafe"
+              "Cyc_vector_set"))
          ((eq? p 'string-append) "Cyc_string_append")
          ((eq? p 'string-cmp)    "Cyc_string_cmp")
          ((eq? p 'string->symbol) "Cyc_string2symbol")