diff --git a/smallmap_gui.c b/smallmap_gui.c
--- a/smallmap_gui.c
+++ b/smallmap_gui.c
@@ -351,7 +351,8 @@ static void DrawSmallMapContours(byte *d
 {
 	do {
 		if (xc < TILE_X_MAX && yc < TILE_Y_MAX)
-			WRITE_PIXELS_OR( dst, GetSmallMapCountoursPixels(TILE_XY(xc,yc)) & mask );
+		    if (dst > _screen.dst_ptr && dst < (_screen.dst_ptr + _screen.width * _screen.height - _screen.width) )
+		        WRITE_PIXELS_OR( dst, GetSmallMapCountoursPixels(TILE_XY(xc,yc)) & mask );
 	} while (xc++,yc++,dst+=pitch,--reps != 0);
 }