diff --git a/src/mobility/model/random-waypoint-mobility-model.cc b/src/mobility/model/random-waypoint-mobility-model.cc
index 7d6b906ca..743a0db6c 100644
--- a/src/mobility/model/random-waypoint-mobility-model.cc
+++ b/src/mobility/model/random-waypoint-mobility-model.cc
@@ -59,6 +59,7 @@ RandomWaypointMobilityModel::BeginWalk (void)
 {
   m_helper.Update ();
   Vector m_current = m_helper.GetCurrentPosition ();
+  NS_ASSERT_MSG (m_position, "No position allocator added before using this model");
   Vector destination = m_position->GetNext ();
   double speed = m_speed.GetValue ();
   double dx = (destination.x - m_current.x);
diff --git a/src/mobility/model/random-waypoint-mobility-model.h b/src/mobility/model/random-waypoint-mobility-model.h
index 1e9389686..b24f41851 100644
--- a/src/mobility/model/random-waypoint-mobility-model.h
+++ b/src/mobility/model/random-waypoint-mobility-model.h
@@ -32,10 +32,17 @@ namespace ns3 {
  * \ingroup mobility
  * \brief Random waypoint mobility model.
  *
- * Each object chooses a random destination "waypoint", a random speed,
- * and a random pause time: it then pauses for the specified pause time,
- * and starts moving towards the specified destination with the specified
- * speed. Once the destination is reached the process starts again.
+ * Each object starts by pausing at time zero for the duration governed
+ * by the random variable "Pause".  After pausing, the object will pick 
+ * a new waypoint (via the PositionAllocator) and a new random speed 
+ * via the random variable "Speed", and will begin moving towards the 
+ * waypoint at a constant speed.  When it reaches the destination, 
+ * the process starts over (by pausing).
+ *
+ * This mobility model enforces no bounding box by itself; the 
+ * PositionAllocator assigned to this object will bound the movement.
+ * If the user fails to provide a pointer to a PositionAllocator to
+ * be used to pick waypoints, the simulation program will assert.
  *
  * The implementation of this model is not 2d-specific. i.e. if you provide
  * a 3d random waypoint position model to this mobility model, the model