diff --git a/Makefile b/Makefile
--- a/Makefile
+++ b/Makefile
@@ -290,7 +290,7 @@ endif
 # -O	optimize or -O2 fully optimize (O's above 2 are not recommended)
 # -pg	profile - generate profiling data.  See "man gprof" to use this.
 
-CFLAGS=-Wall -Wno-multichar
+CFLAGS=-Wall -Wno-multichar -Wsign-compare
 CDEFS=-DWITH_REV
 LDFLAGS=
 LIBS=
diff --git a/map.c b/map.c
--- a/map.c
+++ b/map.c
@@ -29,7 +29,7 @@ TileIndex TileAdd(TileIndex tile, TileIn
 	uint y;
 
 	dx = add & MapMaxX();
-	if (dx >= MapSizeX() / 2) dx -= MapSizeX();
+	if (dx >= (int)MapSizeX() / 2) dx -= MapSizeX();
 	dy = (add - dx) / (int)MapSizeX();
 
 	x = TileX(tile) + dx;