--- src/bits.c.orig	2026-10-20 02:45:42
+++ src/bits.c	2026-10-20 02:45:42
@@ -4001,7 +4001,10 @@
       color->rgb &= 0x00FFFFFF;
       switch (color->method)
         {
-        case 0x0:
+        case 0x0: // no method byte: a plain ACI colour, keep its index
+          if (color->index > 256)
+            color->index = 256;
+          break;
         case 0xc0:
           color->index = 256;
           break; // ByLayer