diff --git a/lib/rmg/ObstaclePlacer.cpp b/lib/rmg/ObstaclePlacer.cpp
index 29fba34ab..bb4c7e042 100644
--- a/lib/rmg/ObstaclePlacer.cpp
+++ b/lib/rmg/ObstaclePlacer.cpp
@@ -24,7 +24,7 @@
 #include "Functions.h"
 #include "../mapping/CMapEditManager.h"
 
-void ObstacleProxy::collectPossibleObstacles(const Terrain & terrain)
+void ObstacleProxy::collectPossibleObstacles(TTerrain terrain)
 {
 	//get all possible obstacles for this terrain
 	for(auto primaryID : VLC->objtypeh->knownObjects())
diff --git a/lib/rmg/ObstaclePlacer.h b/lib/rmg/ObstaclePlacer.h
index b98d042aa..e61df728f 100644
--- a/lib/rmg/ObstaclePlacer.h
+++ b/lib/rmg/ObstaclePlacer.h
@@ -23,7 +23,7 @@ public:
 
 	rmg::Area blockedArea;
 
-	void collectPossibleObstacles(const Terrain & terrain);
+	void collectPossibleObstacles(TTerrain terrain);
 
 	void placeObstacles(CMap * map, CRandomGenerator & rand);