diff --git a/src/character.h b/src/character.h
index 1f21b2ad330..bc65759aa2a 100644
--- a/src/character.h
+++ b/src/character.h
@@ -57,7 +57,8 @@ INLINE_HEADER_BEGIN
 
 /* Minimum leading code of multibyte characters.  */
 #define MIN_MULTIBYTE_LEADING_CODE 0xC0
-/* Maximum leading code of multibyte characters.  */
+/* Maximum leading code of multibyte characters.  Note: this must be
+   updated if we ever increase MAX_CHAR above.  */
 #define MAX_MULTIBYTE_LEADING_CODE 0xF8
 
 /* Unicode character values.  */
diff --git a/src/coding.c b/src/coding.c
index e756ba169dd..b1eb2edb497 100644
--- a/src/coding.c
+++ b/src/coding.c
@@ -1225,7 +1225,10 @@ detect_coding_utf_8 (struct coding_system *coding,
       ONE_MORE_BYTE (c4);
       if (c4 < 0 || ! UTF_8_EXTRA_OCTET_P (c4))
 	break;
-      if (UTF_8_5_OCTET_LEADING_P (c))
+      if (UTF_8_5_OCTET_LEADING_P (c)
+	  /* If we ever need to increase MAX_CHAR, the below may need
+	     to be reviewed.  */
+	  && c < MAX_MULTIBYTE_LEADING_CODE)
 	{
 	  nchars++;
 	  continue;