diff --git a/ObjectTypes/PolyLine/PolyLineT.cc b/ObjectTypes/PolyLine/PolyLineT.cc
index a48d40e3358e6f96b5d7a48a80e505a414c6de46..68bc173e8986694afcef023846a329acfab374d1 100644
--- a/ObjectTypes/PolyLine/PolyLineT.cc
+++ b/ObjectTypes/PolyLine/PolyLineT.cc
@@ -2282,7 +2282,7 @@ void PolyLineT<PointT>::
 
   if (_property_handle) {
 
-    CustomProperty* p = custom_prop(_property_handle);
+    const CustomProperty* p = custom_prop(_property_handle);
 
     unsigned int offset = p->prop_size * _i;