diff --git a/src/unicode.c b/src/unicode.c
index 3bd59ca..376e700 100644
--- a/src/unicode.c
+++ b/src/unicode.c
@@ -465,7 +465,7 @@ int tsm_utf8_mach_feed(struct tsm_utf8_mach *mach, char ci)
 uint32_t tsm_utf8_mach_get(struct tsm_utf8_mach *mach)
 {
 	if (!mach || mach->state != TSM_UTF8_ACCEPT)
-		return KMSCON_UCS4_INVALID;
+		return TSM_UCS4_REPLACEMENT;
 
 	return mach->ch;
 }
diff --git a/src/unicode.h b/src/unicode.h
index 5a69710..3b69e64 100644
--- a/src/unicode.h
+++ b/src/unicode.h
@@ -51,6 +51,10 @@
 #include <inttypes.h>
 #include <stdlib.h>
 
+#define TSM_UCS4_MAX (0x7fffffffUL)
+#define TSM_UCS4_INVALID (TSM_UCS4_MAX + 1)
+#define TSM_UCS4_REPLACEMENT (0xfffdUL)
+
 /* symbols */
 
 typedef uint32_t kmscon_symbol_t;