diff --git a/com.unity.ml-agents.extensions/Editor/RigidBodySensorComponentEditor.cs b/com.unity.ml-agents.extensions/Editor/RigidBodySensorComponentEditor.cs
index 79a17cf4ef..f1606595fb 100644
--- a/com.unity.ml-agents.extensions/Editor/RigidBodySensorComponentEditor.cs
+++ b/com.unity.ml-agents.extensions/Editor/RigidBodySensorComponentEditor.cs
@@ -16,6 +16,16 @@ public override void OnInspectorGUI()
             so.Update();
 
             var rbSensorComp = so.targetObject as RigidBodySensorComponent;
+            if (rbSensorComp.IsTrivial())
+            {
+                EditorGUILayout.HelpBox(
+                    "The Root Body has no Joints, and the Virtual Root is null or the same as the " +
+                    "Root Body's GameObject. This will not generate any useful observations; they will always " +
+                    "be the identity values. Consider removing this component since it won't help the Agent.",
+                    MessageType.Warning
+                );
+            }
+
             bool requireExtractorUpdate;
 
             EditorGUI.BeginDisabledGroup(!EditorUtilities.CanUpdateModelProperties());
diff --git a/com.unity.ml-agents.extensions/Runtime/Sensors/RigidBodySensorComponent.cs b/com.unity.ml-agents.extensions/Runtime/Sensors/RigidBodySensorComponent.cs
index e201125bff..a6dad23b66 100644
--- a/com.unity.ml-agents.extensions/Runtime/Sensors/RigidBodySensorComponent.cs
+++ b/com.unity.ml-agents.extensions/Runtime/Sensors/RigidBodySensorComponent.cs
@@ -91,6 +91,24 @@ internal void SetPoseEnabled(int index, bool enabled)
         {
             GetPoseExtractor().SetPoseEnabled(index, enabled);
         }
+
+        internal bool IsTrivial()
+        {
+            if (ReferenceEquals(RootBody, null))
+            {
+                // It *is* trivial, but this will happen when the sensor is being set up, so don't warn then.
+                return false;
+            }
+            var joints = RootBody.GetComponentsInChildren<Joint>();
+            if (joints.Length == 0)
+            {
+                if (ReferenceEquals(VirtualRoot, null) || ReferenceEquals(VirtualRoot, RootBody.gameObject))
+                {
+                    return true;
+                }
+            }
+            return false;
+        }
     }
 
 }
diff --git a/com.unity.ml-agents.extensions/Tests/Runtime/Sensors/RigidBodySensorTests.cs b/com.unity.ml-agents.extensions/Tests/Runtime/Sensors/RigidBodySensorTests.cs
index 2e1a6fb81b..28fbe95e74 100644
--- a/com.unity.ml-agents.extensions/Tests/Runtime/Sensors/RigidBodySensorTests.cs
+++ b/com.unity.ml-agents.extensions/Tests/Runtime/Sensors/RigidBodySensorTests.cs
@@ -31,6 +31,7 @@ public void TestNullRootBody()
             var gameObj = new GameObject();
 
             var sensorComponent = gameObj.AddComponent<RigidBodySensorComponent>();
+            Assert.IsFalse(sensorComponent.IsTrivial());
             var sensor = sensorComponent.CreateSensors()[0];
             SensorTestHelper.CompareObservation(sensor, new float[0]);
         }
@@ -48,6 +49,7 @@ public void TestSingleRigidbody()
                 UseLocalSpaceTranslations = true,
                 UseLocalSpaceRotations = true
             };
+            Assert.IsTrue(sensorComponent.IsTrivial());
 
             var sensor = sensorComponent.CreateSensors()[0];
             sensor.Update();
@@ -93,6 +95,7 @@ public void TestBodiesWithJoint()
                 UseLocalSpaceLinearVelocity = true
             };
             sensorComponent.VirtualRoot = virtualRoot;
+            Assert.IsFalse(sensorComponent.IsTrivial());
 
             var sensor = sensorComponent.CreateSensors()[0];
             sensor.Update();
diff --git a/com.unity.ml-agents/CHANGELOG.md b/com.unity.ml-agents/CHANGELOG.md
index 6c5be75aa8..b11a00b1f3 100755
--- a/com.unity.ml-agents/CHANGELOG.md
+++ b/com.unity.ml-agents/CHANGELOG.md
@@ -14,6 +14,7 @@ and this project adheres to
 #### ml-agents / ml-agents-envs / gym-unity (Python)
 - Added a fully connected visual encoder for environments with very small image inputs. (#5351)
 ### Bug Fixes
+- RigidBodySensorComponent now displays a warning if it's used in a way that won't generate useful observations. (#5387)
 
 
 ## [2.0.0-exp.1] - 2021-04-22