diff --git a/src/vcl/ldp_glibc_socket.h b/src/vcl/ldp_glibc_socket.h
index 95fb7c8..dcd3720 100644
--- a/src/vcl/ldp_glibc_socket.h
+++ b/src/vcl/ldp_glibc_socket.h
@@ -200,15 +200,14 @@
 extern ssize_t
 sendmsg (int __fd, const struct msghdr *__message, int __flags);
 
-#ifdef __USE_GNU
+#ifdef _GNU_SOURCE
 /* Send a VLEN messages as described by VMESSAGES to socket FD.
    Returns the number of datagrams successfully written or -1 for errors.
 
    This function is a cancellation point and therefore not marked with
    __THROW.  */
-extern int
-sendmmsg (int __fd, struct mmsghdr *__vmessages,
-	  unsigned int __vlen, int __flags);
+extern int sendmmsg (int __fd, struct mmsghdr *__vmessages,
+		     unsigned int __vlen, int __flags);
 #endif
 
 /* Receive a message as described by MESSAGE from socket FD.
@@ -218,7 +217,7 @@
    __THROW.  */
 extern ssize_t recvmsg (int __fd, struct msghdr *__message, int __flags);
 
-#ifdef __USE_GNU
+#ifdef _GNU_SOURCE
 /* Receive up to VLEN messages as described by VMESSAGES from socket FD.
    Returns the number of messages received or -1 for errors.
 
@@ -337,7 +336,7 @@
    __THROW.  */
 extern int poll (struct pollfd *__fds, nfds_t __nfds, int __timeout);
 
-#ifdef __USE_GNU
+#ifdef _GNU_SOURCE
 /* Like poll, but before waiting the threads signal mask is replaced
    with that specified in the fourth parameter.  For better usability,
    the timeout value is specified using a TIMESPEC object.