diff --git a/tests/usr.bin/xlint/lint1/lex_char_uchar.c b/tests/usr.bin/xlint/lint1/lex_char_uchar.c
index 9c91b9bb1559..25d0fe1a096b 100644
--- a/tests/usr.bin/xlint/lint1/lex_char_uchar.c
+++ b/tests/usr.bin/xlint/lint1/lex_char_uchar.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: lex_char_uchar.c,v 1.1 2021/06/29 13:58:13 rillig Exp $	*/
+/*	$NetBSD: lex_char_uchar.c,v 1.2 2021/06/29 14:19:51 rillig Exp $	*/
 # 3 "lex_char_uchar.c"
 
 /*
@@ -11,6 +11,7 @@
 /*
  * FIXME: The warning is bogus; it must be possible to initialize a char
  *  variable with a character constant.
+ * See tree.c, function convert_constant.
  */
 /* expect+1: conversion of 'int' to 'char' is out of range [119] */
 char ch = '\xff';
diff --git a/tests/usr.bin/xlint/lint1/lex_char_uchar.exp b/tests/usr.bin/xlint/lint1/lex_char_uchar.exp
index 6985a5eda79f..e8e2ccfb9c6a 100644
--- a/tests/usr.bin/xlint/lint1/lex_char_uchar.exp
+++ b/tests/usr.bin/xlint/lint1/lex_char_uchar.exp
@@ -1 +1 @@
-lex_char_uchar.c(16): warning: conversion of 'int' to 'char' is out of range [119]
+lex_char_uchar.c(17): warning: conversion of 'int' to 'char' is out of range [119]
diff --git a/usr.bin/xlint/lint1/tree.c b/usr.bin/xlint/lint1/tree.c
index aeb3a97e85f4..271593d4f211 100644
--- a/usr.bin/xlint/lint1/tree.c
+++ b/usr.bin/xlint/lint1/tree.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: tree.c,v 1.295 2021/06/29 10:12:35 rillig Exp $	*/
+/*	$NetBSD: tree.c,v 1.296 2021/06/29 14:19:51 rillig Exp $	*/
 
 /*
  * Copyright (c) 1994, 1995 Jochen Pohl
@@ -37,7 +37,7 @@
 
 #include <sys/cdefs.h>
 #if defined(__RCSID) && !defined(lint)
-__RCSID("$NetBSD: tree.c,v 1.295 2021/06/29 10:12:35 rillig Exp $");
+__RCSID("$NetBSD: tree.c,v 1.296 2021/06/29 14:19:51 rillig Exp $");
 #endif
 
 #include <float.h>
@@ -2410,6 +2410,11 @@ convert_constant(op_t op, int arg, const type_t *tp, val_t *nv, val_t *v)
 	case LCOMPLEX:
 		break;
 	default:
+		/*
+		 * FIXME: There must be no sign extension when converting
+		 *  from int to char on a platform where char == unsigned
+		 *  char.  See test lex_char_uchar.c.
+		 */
 		sz = tp->t_bitfield ? tp->t_flen : size_in_bits(nt);
 		nv->v_quad = xsign(nv->v_quad, nt, sz);
 		break;