diff --git a/tools/libtxt/Makefile b/tools/libtxt/Makefile
index 39f80b6..cc3dd0d 100644
--- a/tools/libtxt/Makefile
+++ b/tools/libtxt/Makefile
@@ -13,7 +13,8 @@
 
 LIB = libtxt.a
 
-CFLAGS = -g -Wall
+# _GNU_SOURCE for vasprintf
+CFLAGS = -g -Wall -D_GNU_SOURCE
 
 OBJS = edit.o font.o
 
diff --git a/tools/libtxt/font.c b/tools/libtxt/font.c
index 62ec705..e8d68ff 100644
--- a/tools/libtxt/font.c
+++ b/tools/libtxt/font.c
@@ -11,14 +11,12 @@
  */
 
 
-#define _GNU_SOURCE /* for vasprintf */
-#include <stdarg.h>
 #include <stdint.h>
 #include <stdlib.h>
-#include <stdio.h>
 #include <string.h>
 #include <errno.h>
 
+#include "util.h"
 #include "libtxt.h"
 
 
@@ -45,28 +43,6 @@ struct font {
 };
 
 
-/* ----- Helper functions -------------------------------------------------- */
-
-
-static const char *alloc_sprintf(const char *fmt, ...)
-{
-	va_list ap;
-	char *tmp, *res;
-	int n;
-
-	va_start(ap, fmt);
-	n = vasprintf(&tmp, fmt, ap);
-	va_end(ap);
-	if (n < 0)
-		abort();
-	res = malloc(n+1);
-	if (!res)
-		abort();
-	memcpy(res, tmp, n+1);
-	return res;
-}
-
-
 /* ----- XBM image --------------------------------------------------------- */
 
 
diff --git a/tools/libtxt/util.h b/tools/libtxt/util.h
new file mode 100644
index 0000000..8d77b52
--- /dev/null
+++ b/tools/libtxt/util.h
@@ -0,0 +1,40 @@
+/*
+ * tools/libtxt/util.h - Utility functions
+ *
+ * Written 2012 by Werner Almesberger
+ * Copyright 2012 Werner Almesberger
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+#ifndef UTIL_H
+#define UTIL_H
+
+#include <stdarg.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+
+
+static const char *alloc_sprintf(const char *fmt, ...)
+{
+	va_list ap;
+	char *tmp, *res;
+	int n;
+
+	va_start(ap, fmt);
+	n = vasprintf(&tmp, fmt, ap);
+	va_end(ap);
+	if (n < 0)
+		abort();
+	res = malloc(n+1);
+	if (!res)
+		abort();
+	memcpy(res, tmp, n+1);
+	return res;
+}
+
+#endif /* !UTIL_H */