diff --git a/src/main/java/com/jme3/bullet/PhysicsSpace.java b/src/main/java/com/jme3/bullet/PhysicsSpace.java
index ca23d623..540cd0a6 100644
--- a/src/main/java/com/jme3/bullet/PhysicsSpace.java
+++ b/src/main/java/com/jme3/bullet/PhysicsSpace.java
@@ -793,7 +793,8 @@ public void setMaxTimeStep(float maxTimeStep) {
 
     /**
      * Update this space. Can be used to single-step the physics simulation, if
-     * maxSubSteps is set to 0 or 1.
+     * maxSubSteps is set to 0 or 1. This method should be invoked from the
+     * thread that created the space.
      *
      * @see #setMaxSubSteps(int)
      * @param timeInterval the time interval to simulate (in seconds, ≥0)
@@ -812,7 +813,8 @@ public void update(float timeInterval) {
     }
 
     /**
-     * Update this space.
+     * Update this space. This method should be invoked from the thread that
+     * created the space.
      *
      * @param timeInterval the time interval to simulate (in seconds, ≥0)
      * @param maxSteps the maximum number of steps of size {@code accuracy}