diff --git a/src/Mono.cs b/src/Mono.cs
index f44743f..5a4a3fa 100644
--- a/src/Mono.cs
+++ b/src/Mono.cs
@@ -101,7 +101,13 @@ static class Mono
 
     public static void Step()
     {
-        if (s_array[snake[0] + snake_dir] > -1)
+        // eat tail
+        if (snake[0] + snake_dir == snake[snake_len-1])
+        {
+            snake_len--;
+            grow_buffer = 0;
+        }
+        else if (s_array[snake[0] + snake_dir] > -1)
         {
             // lose condition
             bool stuck = true;