diff --git a/yapf/yapf_common.cpp b/yapf/yapf_common.cpp
index a0a911cf98..99155c58eb 100644
--- a/yapf/yapf_common.cpp
+++ b/yapf/yapf_common.cpp
@@ -8,6 +8,7 @@
 #include "yapf_costbase.hpp"
 #include "yapf_costcache.hpp"
 
+/** translate tileh to the bitset of up-hill trackdirs */
 const TrackdirBits CYapfCostBase::c_upwards_slopes[] = {
 	TRACKDIR_BIT_NONE                    , // no tileh
 	TRACKDIR_BIT_X_SW | TRACKDIR_BIT_Y_NW, // 1
diff --git a/yapf/yapf_rail.cpp b/yapf/yapf_rail.cpp
index 08ee143ed1..67d3d781fc 100644
--- a/yapf/yapf_rail.cpp
+++ b/yapf/yapf_rail.cpp
@@ -260,6 +260,7 @@ bool YapfFindNearestRailDepotTwoWay(Vehicle *v, int max_distance, int reverse_pe
 	return ret;
 }
 
+/** if any track changes, this counter is incremented - that will invalidate segment cost cache */
 int CSegmentCostCacheBase::s_rail_change_counter = 0;
 
 void YapfNotifyTrackLayoutChange(TileIndex tile, Track track) {CSegmentCostCacheBase::NotifyTrackLayoutChange(tile, track);}