diff --git a/ChangeLog b/ChangeLog
index d8b7ff6559..6145b67156 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,10 @@
 2026-09-20  Bruno Haible  <bruno@clisp.org>
 
+	wctob: Make consistent with wcrtomb.
+	* m4/wctob.m4 (gl_FUNC_WCTOB): Require gl_MBRTOWC_C_LOCALE and, if
+	needed, set REPLACE_WCTOB.
+	* modules/wctob (Files): Add mbrtowc.m4.
+
 	wctob: Make thread-safe if possible.
 	* m4/wctob.m4 (gl_PREREQ_WCTOB): Test for wcrtomb.
 	* lib/wctob.c (wctob): Use wcrtomb instead of wctomb if possible.
diff --git a/m4/wctob.m4 b/m4/wctob.m4
index 0fcb560aaf..127fd18dc5 100644
--- a/m4/wctob.m4
+++ b/m4/wctob.m4
@@ -1,5 +1,5 @@
 # wctob.m4
-# serial 16
+# serial 17
 dnl Copyright (C) 2008-2026 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -91,6 +91,14 @@ int main ()
       *yes) ;;
       *) REPLACE_WCTOB=1 ;;
     esac
+    dnl When we adjust mbrtowc in the C locale, we need to adjust wctob as well,
+    dnl for consistency.
+    AC_REQUIRE([gl_MBRTOWC_C_LOCALE])
+    case "$gl_cv_func_mbrtowc_C_locale_sans_EILSEQ" in
+      *yes) ;;
+      *) REPLACE_WCTOB=1
+         ;;
+    esac
   fi
 ])
 
diff --git a/modules/wctob b/modules/wctob
index 35e6e8be0d..cfd3b898d1 100644
--- a/modules/wctob
+++ b/modules/wctob
@@ -4,6 +4,7 @@ wctob() function: convert wide character to unibyte character.
 Files:
 lib/wctob.c
 m4/wctob.m4
+m4/mbrtowc.m4
 m4/locale-en.m4
 m4/locale-fr.m4
 m4/codeset.m4