diff --git a/src/libmittos/graphics/graphics.c b/src/libmittos/graphics/graphics.c
index 128589e..0b2859b 100644
--- a/src/libmittos/graphics/graphics.c
+++ b/src/libmittos/graphics/graphics.c
@@ -35,7 +35,9 @@ void draw_line(
   int64_t diff = dx - dy;
   uint32_t *fb = (uint32_t *)ctx->buffer;
   while(1) {
-    fb[PXL(ctx, x, y)] = clr;
+    if(0 < x && x < ctx->width &&
+        0 < y && y < ctx->height)
+      fb[PXL(ctx, x, y)] = clr;
     if(x == x1 && y == y1) break;
 
     if((2*diff) > -dy) {