diff --git a/m4/absolute-header.m4 b/m4/absolute-header.m4
index dba8dbf..eead483 100644
--- a/m4/absolute-header.m4
+++ b/m4/absolute-header.m4
@@ -70,8 +70,8 @@ AC_DEFUN([gl_ABSOLUTE_HEADER_ONE],
   dnl so use subshell.
   AS_VAR_SET([gl_cv_absolute_]AS_TR_SH([[$1]]),
 [`(eval "$gl_absname_cpp conftest.$ac_ext") 2>&AS_MESSAGE_LOG_FD |
-sed -n '\#/$1#{
-        s#.*"\(.*/$1\)".*#\1#
+sed -n '\#[/\\]$1#{
+        s#.*"\(.*[\\/]$1\)".*#\1#
         s#^/[^/]#//&#
         p
         q