diff --git a/Tremolo/floor1.c b/Tremolo/floor1.c
index a2a035b..4a4937d 100644
--- a/Tremolo/floor1.c
+++ b/Tremolo/floor1.c
@@ -232,8 +232,9 @@
 
   if(n>x1)n=x1;
   n -= x0;
-  if (n <= 0)
+  if (n <= 0 || y0 < 0 || y0 > 255 || y1 < 0 || y1 > 255) {
     return;
+  }
   dy=y1-y0;
   adx=x1-x0;
   ady=abs(dy);