diff --git a/compact/definitions.xml b/compact/definitions.xml
index 908de8a96403addcbb4cd8ff73ac60d9724fbd04..7c71e90f4f85b8bb546dd69316350566dd540c28 100644
--- a/compact/definitions.xml
+++ b/compact/definitions.xml
@@ -346,6 +346,8 @@ Examples:
     <documentation>
       ### Tracker Detector Parameters
       TrackerBarrel_rmax: also the rmin for the barrel PID system (DIRC)
+      Note: The barrel rmax and endcap lengths are the maximum extent allowed for
+      the barrel and endcap layers, not the position of the final layer.
     </documentation>
 
     <constant name="TrackerBarrel_rmin"         value="VertexTrackingRegion_rmax"/>