diff --git a/src/asm/main.c b/src/asm/main.c
index 46194cfd..62ed48f6 100644
--- a/src/asm/main.c
+++ b/src/asm/main.c
@@ -5,8 +5,8 @@
  *
  */
 
+#define _XOPEN_SOURCE 500
 #include <math.h>
-#include <getopt.h>
 #include <stdarg.h>
 #include <stdbool.h>
 #include <stdio.h>
diff --git a/src/fix/main.c b/src/fix/main.c
index 36cc2df9..d1d4a35d 100644
--- a/src/fix/main.c
+++ b/src/fix/main.c
@@ -14,7 +14,7 @@
  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
-#include <getopt.h>
+#define _XOPEN_SOURCE 500
 #include <stdbool.h>
 #include <stdint.h>
 #include <stdio.h>
diff --git a/src/link/main.c b/src/link/main.c
index 84ecb8f6..a5e54b60 100644
--- a/src/link/main.c
+++ b/src/link/main.c
@@ -1,4 +1,4 @@
-#include <getopt.h>
+#define _XOPEN_SOURCE 500
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>