diff --git a/ports/unix/moduselect.c b/ports/unix/moduselect.c
index 4fa8d3ae80..a95663e31f 100644
--- a/ports/unix/moduselect.c
+++ b/ports/unix/moduselect.c
@@ -158,13 +158,13 @@ STATIC mp_obj_t poll_modify(mp_obj_t self_in, mp_obj_t obj_in, mp_obj_t eventmas
     for (int i = self->len - 1; i >= 0; i--) {
         if (entries->fd == fd) {
             entries->events = mp_obj_get_int(eventmask_in);
-            break;
+            return mp_const_none;
         }
         entries++;
     }
 
-    // TODO raise KeyError if obj didn't exist in map
-    return mp_const_none;
+    // obj doesn't exist in poller
+    mp_raise_OSError(MP_ENOENT);
 }
 MP_DEFINE_CONST_FUN_OBJ_3(poll_modify_obj, poll_modify);