diff --git a/.gitattributes b/.gitattributes
index 3f96162..3827ab4 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -6,8 +6,8 @@ Makefile.am			ident
 /data/trader.svg		ident
 /doc/trader.*			ident
 /lib/obsolete-strings.c		ident
-/lib/xopen_source.h		ident
-/m4/xopen_source.m4		ident
+/lib/xopen-source.h		ident
+/m4/xopen-source.m4		ident
 /po/LINGUAS			ident
 /po/Makevars			ident
 /po/POTFILES.in			ident
diff --git a/Makefile.am b/Makefile.am
index 92eb9a2..ec75eb4 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -35,4 +35,4 @@ EXTRA_DIST = \
 	build-aux/bootstrap		\
 	build-aux/msgfmt-desktop	\
 	lib/obsolete-strings.c		\
-	lib/xopen_source.h
+	lib/xopen-source.h
diff --git a/lib/README b/lib/README
index e14305d..3ef17b4 100644
--- a/lib/README
+++ b/lib/README
@@ -9,10 +9,10 @@ This directory, lib,  contains source code as generated  by the Gnulib GNU
 Portability  Library "gnulib-tool" script.   See the  project web  site at
 https://www.gnu.org/software/gnulib/ for more information.
 
-The following file is used by  xopen_source.m4  to redefine  _XOPEN_SOURCE
+The following file is used by  xopen-source.m4  to redefine  _XOPEN_SOURCE
 appropriately.  It is not part of the GNU Portability Library:
 
-    xopen_source.h
+    xopen-source.h
 
 The following file provides translatable strings  for obsolete versions of
 various libraries.  It is not part of the GNU Portability Library:
diff --git a/lib/xopen_source.h b/lib/xopen-source.h
similarity index 92%
rename from lib/xopen_source.h
rename to lib/xopen-source.h
index f8d1b63..4b23b4c 100644
--- a/lib/xopen_source.h
+++ b/lib/xopen-source.h
@@ -9,9 +9,9 @@
   Author: John Zaitseff <J.Zaitseff@zap.org.au>
   $Id$
 
-  This file, xopen_source.h, redefines _XOPEN_SOURCE to be the latest
+  This file, xopen-source.h, redefines _XOPEN_SOURCE to be the latest
   version that is supported by the operating system's C library.  It is
-  used by the Autoconf macro in m4/xopen_source.m4.
+  used by the Autoconf macro in m4/xopen-source.m4.
 
 
   This program is free software: you can redistribute it and/or modify it
diff --git a/m4/Makefile.am b/m4/Makefile.am
index da5404f..18d5cf1 100644
--- a/m4/Makefile.am
+++ b/m4/Makefile.am
@@ -36,4 +36,4 @@ EXTRA_DIST = \
 	ax_require_defined.m4	\
 	ax_with_curses.m4	\
 	gnulib-cache.m4		\
-	xopen_source.m4
+	xopen-source.m4
diff --git a/m4/README b/m4/README
index 159de51..38356b6 100644
--- a/m4/README
+++ b/m4/README
@@ -9,7 +9,7 @@ This directory, m4, contains M4 macros used by Autoconf.
 
 The following macros are custom-defined for Star Traders:
 
-    xopen_source.m4
+    xopen-source.m4
 
 The following macros are from the Autoconf Archive project, as detailed on
 that project's web site, https://www.gnu.org/software/autoconf-archive/:
diff --git a/m4/xopen_source.m4 b/m4/xopen-source.m4
similarity index 96%
rename from m4/xopen_source.m4
rename to m4/xopen-source.m4
index b5b582b..a9c2fe3 100644
--- a/m4/xopen_source.m4
+++ b/m4/xopen-source.m4
@@ -12,7 +12,7 @@
 # latest version of _XOPEN_SOURCE supported by the C library.  It does
 # this by compiling code with various values of that symbol.  Once a
 # particular value compiles without error, it redefines _XOPEN_SOURCE to
-# that value using the auxiliary file <lib/xopen_source.h> and sets
+# that value using the auxiliary file <lib/xopen-source.h> and sets
 # $x_cv_latest_xopen_source to one of the following values:
 #
 #   700       - _XOPEN_SOURCE=700 (for SUSv4 / XPG7) was accepted
@@ -45,7 +45,7 @@ AC_DEFUN([USE_LATEST_XOPEN_SOURCE], [dnl
     AC_REQUIRE([gl_USE_SYSTEM_EXTENSIONS])
     AH_BOTTOM([
 /* Redefine _XOPEN_SOURCE as required */
-@%:@include <xopen_source.h>
+@%:@include <xopen-source.h>
 ])
     AC_CACHE_CHECK([the latest supported version of _XOPEN_SOURCE],
 	[x_cv_latest_xopen_source], [