diff --git a/src/xpath.c b/src/xpath.c
index 88403a0..c8beb28 100644
--- a/src/xpath.c
+++ b/src/xpath.c
@@ -12,6 +12,7 @@
  *     https://opensource.org/licenses/BSD-3-Clause
  */
 #define _GNU_SOURCE
+#define _POSIX_C_SOURCE 200809L /* strdup, strndup */
 
 /* needed by libmath functions isfinite(), isinf(), isnan(), signbit(), ... */
 #define _ISOC99_SOURCE