diff --git a/sim.c b/sim.c
index 68bbba2..bc9e6dc 100644
--- a/sim.c
+++ b/sim.c
@@ -304,7 +304,7 @@ BEGIN_SOLO_PHASE_0(comment)
   if (!IS_AWAKE)
     return;
   Glyph* line = gbuffer + y * width;
-  Usz max_x = width < 255 ? width : 255;
+  Usz max_x = width < x + 255 ? width : x + 255;
   for (Usz x0 = x + 1; x0 < max_x; ++x0) {
     Glyph g = line[x0];
     mbuffer_poke_flags_or(mbuffer, height, width, y, x0, Mark_flag_lock);