diff --git a/sixteen.c b/sixteen.c
index b44e925..aa10f4a 100644
--- a/sixteen.c
+++ b/sixteen.c
@@ -762,11 +762,11 @@ static game_state *execute_move(const game_state *from, const char *move)
     }
 
     if (move[0] == 'R' && sscanf(move+1, "%d,%d", &cy, &dx) == 2 &&
-	cy >= 0 && cy < from->h) {
+	cy >= 0 && cy < from->h && -from->h <= dx && dx <= from->w ) {
 	cx = dy = 0;
 	n = from->w;
     } else if (move[0] == 'C' && sscanf(move+1, "%d,%d", &cx, &dy) == 2 &&
-	       cx >= 0 && cx < from->w) {
+	       cx >= 0 && cx < from->w && -from->h <= dy && dy <= from->h) {
 	cy = dx = 0;
 	n = from->h;
     } else