diff --git a/src/script/api/script_road.cpp b/src/script/api/script_road.cpp
--- a/src/script/api/script_road.cpp
+++ b/src/script/api/script_road.cpp
@@ -245,7 +245,7 @@ static int32 LookupWithBuildOnSlopes(::S
 
 	/* Now perform the actual rotation. */
 	for (int j = 0; j < base_rotate; j++) {
-		for (int i = 0; i < existing->size; i++) {
+		for (size_t i = 0; i < existing->size; i++) {
 			existing->array[i] = RotateNeighbour(existing->array[i]);
 		}
 		start = RotateNeighbour(start);
@@ -256,7 +256,7 @@ static int32 LookupWithBuildOnSlopes(::S
 	RoadBits start_roadbits    = NeighbourToRoadBits(start);
 	RoadBits new_roadbits      = start_roadbits | NeighbourToRoadBits(end);
 	RoadBits existing_roadbits = ROAD_NONE;
-	for (int i = 0; i < existing->size; i++) {
+	for (size_t i = 0; i < existing->size; i++) {
 		existing_roadbits |= NeighbourToRoadBits(existing->array[i]);
 	}
 
@@ -354,7 +354,7 @@ static bool NormaliseTileOffset(int32 *t
 	/* The start tile and end tile cannot be the same tile either. */
 	if (start == end) return -1;
 
-	for (int i = 0; i < existing->size; i++) {
+	for (size_t i = 0; i < existing->size; i++) {
 		if (!NormaliseTileOffset(&existing->array[i])) return -1;
 	}