diff --git a/library/entropy_poll.c b/library/entropy_poll.c
index 4bf660e..5250a7b 100644
--- a/library/entropy_poll.c
+++ b/library/entropy_poll.c
@@ -17,7 +17,7 @@
  *  limitations under the License.
  */
 
-#if defined(__linux__)
+#if defined(__linux__) && !defined(_GNU_SOURCE)
 /* Ensure that syscall() is available even when compiling with -std=c99 */
 #define _GNU_SOURCE
 #endif