diff --git a/tek4010.c b/tek4010.c
index 8da294a..c796c45 100755
--- a/tek4010.c
+++ b/tek4010.c
@@ -38,6 +38,8 @@
                                 
 #define PI2 6.283185307
 
+#define _GNU_SOURCE
+
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>