diff --git a/src/Mono.cs b/src/Mono.cs
index fca97db..a60c14b 100644
--- a/src/Mono.cs
+++ b/src/Mono.cs
@@ -89,6 +89,32 @@ static class Mono
             return;
         }
 
+        XYZi next_pos = snake[0] + snake_dir;
+        bool around_box = false;
+        for (int i = 0; i < directions.Length; i++)
+        {
+            if (s_array.InRange(next_pos + directions[i]))
+            {
+                around_box = true;
+                break;
+            }
+        }
+        if (!around_box)
+        {
+            for (int i = 0; i < corners.Length; i++)
+            {
+                if (s_array.InRange(next_pos + corners[i]))
+                {
+                    around_box = true;
+                    break;
+                }
+            }
+        }
+        if (!around_box)
+        {
+            return;
+        }
+
         if (snake_len == snake.Length)
         {
             // win condition