diff --git a/build-aux/configure-lib.sh b/build-aux/configure-lib.sh
index 82756a5f..e1da64f0 100644
--- a/build-aux/configure-lib.sh
+++ b/build-aux/configure-lib.sh
@@ -323,6 +323,7 @@ lib/dirent/readdir.c
 lib/math/ceil.c
 lib/math/fabs.c
 lib/math/floor.c
+lib/math/labs.c
 lib/mes/fdgets.c
 lib/posix/alarm.c
 lib/posix/execl.c
diff --git a/include/math.h b/include/math.h
index 2e2ca985..fe5801b7 100644
--- a/include/math.h
+++ b/include/math.h
@@ -31,6 +31,7 @@ double cos (double x);
 double exp (double x);
 double fabs (double number);
 double floor (double x);
+long int labs (long int number);
 double ldexp (double value, int exponent);
 double log (double x);
 double modf (double value, double *integer_part);
diff --git a/lib/math/labs.c b/lib/math/labs.c
new file mode 100644
index 00000000..62a8a6f0
--- /dev/null
+++ b/lib/math/labs.c
@@ -0,0 +1,29 @@
+/* -*-comment-start: "//";comment-end:""-*-
+ * GNU Mes --- Maxwell Equations of Software
+ * Copyright © 2019 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
+ *
+ * This file is part of GNU Mes.
+ *
+ * GNU Mes 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 3 of the License, or (at
+ * your option) any later version.
+ *
+ * GNU Mes is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with GNU Mes.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <math.h>
+
+long int
+labs (long int number)
+{
+  if (number < 0)
+    return -number;
+  return number;
+}