diff --git a/osi_object.proto b/osi_object.proto
index 5b5317485..8171e1143 100644
--- a/osi_object.proto
+++ b/osi_object.proto
@@ -21,7 +21,7 @@ message StationaryObject
     //
     optional Identifier id = 1;
 
-    // The base parameters of the vehicle.
+    // The base parameters of the stationary object.
     //
     optional BaseStationary base = 2;
 
@@ -29,6 +29,12 @@ message StationaryObject
     //
     optional Classification classification = 3;
 
+    // Opaque reference of an associated 3D model of the stationary object.
+    //
+    // \note It is implementation-specific how model_references are resolved to 3d models.
+    //
+    optional string model_reference = 4;
+
     //
     // \brief Classification data for a stationary object.
     //
@@ -308,6 +314,12 @@ message MovingObject
     //
     optional VehicleClassification vehicle_classification = 6;
 
+    // Opaque reference of an associated 3D model of the moving object.
+    //
+    // \note It is implementation-specific how model_references are resolved to 3d models.
+    //
+    optional string model_reference = 7;
+
     // Definition of object types.
     //
     enum Type