diff --git a/data/bison.m4 b/data/bison.m4
index 87ad0ca1..6dde067d 100644
--- a/data/bison.m4
+++ b/data/bison.m4
@@ -65,14 +65,16 @@ version 2.2 of Bison.])])
 ## Output.  ##
 ## -------- ##
 
-# b4_output_begin(FILE)
-# ---------------------
+# b4_output_begin(FILE1, FILE2)
+# -----------------------------
 # Enable output, i.e., send to diversion 0, expand after "#", and
 # generate the tag to output into FILE.  Must be followed by EOL.
+# FILE is FILE1 concatenated to FILE2.  FILE2 can be empty, or be
+# absolute: do the right thing.
 m4_define([b4_output_begin],
 [m4_changecom()
 m4_divert_push(0)dnl
-@output(m4_unquote([$1])@)@dnl
+@output(m4_unquote([$1])@,m4_unquote([$2])@)@dnl
 ])
 
 
diff --git a/data/location.cc b/data/location.cc
index 7ebf2f40..9c21cecd 100644
--- a/data/location.cc
+++ b/data/location.cc
@@ -305,7 +305,7 @@ m4_define([b4_location_define],
 
 
 m4_ifdef([b4_position_file], [[
-]b4_output_begin([b4_dir_prefix[]b4_position_file])[
+]b4_output_begin([b4_dir_prefix], [b4_position_file])[
 // Starting with Bison 3.2, this file is useless: the structure it
 // used to define is now defined in "]b4_location_file[".
 //
@@ -323,7 +323,7 @@ m4_ifdef([b4_position_file], [[
 
 
 m4_ifdef([b4_location_file], [[
-]b4_output_begin([b4_dir_prefix[]b4_location_file])[
+]b4_output_begin([b4_dir_prefix], [b4_location_file])[
 ]b4_copyright([Locations for Bison parsers in C++])[
 
 /**
diff --git a/data/stack.hh b/data/stack.hh
index 1946cc48..a8b13b04 100644
--- a/data/stack.hh
+++ b/data/stack.hh
@@ -140,7 +140,7 @@ m4_define([b4_stack_define],
 
 
 m4_ifdef([b4_stack_file],
-[b4_output_begin([b4_dir_prefix[]b4_stack_file])[
+[b4_output_begin([b4_dir_prefix], [b4_stack_file])[
 // Starting with Bison 3.2, this file is useless: the structure it
 // used to define is now defined with the parser itself.
 //
diff --git a/src/scan-skel.l b/src/scan-skel.l
index 096a07ae..63a6dc32 100644
--- a/src/scan-skel.l
+++ b/src/scan-skel.l
@@ -29,8 +29,9 @@
 #define FLEX_PREFIX(Id) skel_ ## Id
 #include <src/flex-scanner.h>
 
-#include <dirname.h>
 #include <error.h>
+#include <dirname.h>
+#include <path-join.h>
 #include <quotearg.h>
 
 #include <src/complain.h>
@@ -236,14 +237,14 @@ at_complain (int argc, char *argv[], char **out_namep, int *out_linenop)
 static void
 at_output (int argc, char *argv[], char **out_namep, int *out_linenop)
 {
-  if (2 < argc)
+  if (3 < argc)
     fail_for_at_directive_too_many_args (argv[0]);
   if (*out_namep)
     {
       free (*out_namep);
       xfclose (yyout);
     }
-  *out_namep = xstrdup (argv[1]);
+  *out_namep = xpath_join (argv[1], 2 < argc ? argv[2] : NULL);
   output_file_name_check (out_namep, true);
   /* If there were errors, do not generate the output.  */
   yyout = xfopen (complaint_status ? "/dev/null" : *out_namep, "w");
diff --git a/tests/output.at b/tests/output.at
index 3ee79df7..2c2cd9b8 100644
--- a/tests/output.at
+++ b/tests/output.at
@@ -45,9 +45,13 @@ done
 [$2[
 %%
 foo: %empty {};
-]])[
+]])
 
-]AT_BISON_CHECK([$3 $1], [$5], [], [ignore])[
+# There is not AT_DATA_UNQUOTED.
+AT_CHECK([$PERL -pi -e 's{\$at_dir}'"{$at_group_dir}g" $1])
+
+
+AT_BISON_CHECK([$3 $1], [$5], [], [ignore])[
 # Ignore the files non-generated files
 ]AT_CHECK_FILES([$4], [$1])[
 ]$6[
@@ -206,8 +210,10 @@ AT_CHECK_OUTPUT([foo.yy],
                 [%skeleton "lalr1.cc" %defines %locations %define api.location.file "foo.loc.hh"],
                 [],
                 [foo.loc.hh foo.tab.cc foo.tab.hh])
+
+# Absolute paths.
 AT_CHECK_OUTPUT([foo.yy],
-                [%skeleton "lalr1.cc" %defines %define api.stack.file none %locations %define api.location.file "foo.loc.hh"],
+                [%skeleton "lalr1.cc" %defines %locations %define api.location.file "$at_dir/foo.loc.hh"],
                 [],
                 [foo.loc.hh foo.tab.cc foo.tab.hh])
 
diff --git a/tests/skeletons.at b/tests/skeletons.at
index 5e99b340..8c180564 100644
--- a/tests/skeletons.at
+++ b/tests/skeletons.at
@@ -306,7 +306,7 @@ use strict;
 my $M4 = "m4";
 my $DNL = "d"."nl";
 print "${M4}_divert_push(0)$DNL\n";
-print '@output(@,@)', "\n";
+print '@output(@,@,@)', "\n";
 (print "garbage"x10, "\n") for (1..1000);
 print "${M4}_divert_pop(0)\n";
 ]])