diff --git a/src/sim65/error.h b/src/sim65/error.h
index 5d6e8be21..cbb785875 100644
--- a/src/sim65/error.h
+++ b/src/sim65/error.h
@@ -49,10 +49,10 @@
 
 
 
-#define SIM65_ERROR         256
+#define SIM65_ERROR         0x7F
 /* Does not use EXIT_FAILURE because it may overlap with test results. */
 
-#define SIM65_ERROR_TIMEOUT 257
+#define SIM65_ERROR_TIMEOUT 0x7E
 /* An error result for max CPU instructions exceeded. */