diff --git a/constants/collision_constants.asm b/constants/collision_constants.asm
index 86fdf9384..b693dc8f8 100644
--- a/constants/collision_constants.asm
+++ b/constants/collision_constants.asm
@@ -113,3 +113,5 @@ HI_NYBBLE_WALK       EQU $40
 HI_NYBBLE_WALK_ALT   EQU $50
 HI_NYBBLE_WARPS      EQU $70
 HI_NYBBLE_LEDGES     EQU $a0
+HI_NYBBLE_SIDE_WALLS EQU $b0
+HI_NYBBLE_UNUSED_C0  EQU $c0
diff --git a/engine/overworld/npc_movement.asm b/engine/overworld/npc_movement.asm
index b21e46700..b4b5ef467 100644
--- a/engine/overworld/npc_movement.asm
+++ b/engine/overworld/npc_movement.asm
@@ -142,9 +142,9 @@ Function6f5f:
 Function6f7f:
 	ld d, a
 	and $f0
-	cp $b0
+	cp HI_NYBBLE_SIDE_WALLS
 	jr z, .done
-	cp $c0
+	cp HI_NYBBLE_UNUSED_C0
 	jr z, .done
 	xor a
 	ret
diff --git a/home/map.asm b/home/map.asm
index ce4dad58c..550486081 100644
--- a/home/map.asm
+++ b/home/map.asm
@@ -1643,9 +1643,9 @@ GetMovementPermissions::
 
 .CheckHiNybble:
 	and $f0
-	cp $b0
+	cp HI_NYBBLE_SIDE_WALLS
 	ret z
-	cp $c0
+	cp HI_NYBBLE_UNUSED_C0
 	ret
 
 GetFacingTileCoord::