diff --git a/include/fcntl.h b/include/fcntl.h
index b014662..27ca147 100644
--- a/include/fcntl.h
+++ b/include/fcntl.h
@@ -9,7 +9,7 @@ extern "C" {
 #define __NEED_pid_t
 #define __NEED_mode_t
 
+#ifdef _GNU_SOURCE
+#define __NEED_size_t
 #define __NEED_ssize_t
 #endif
@@ -102,10 +102,10 @@ int posix_fallocate(int, off_t, off_t);
 #define F_TEST  3
 
 int lockf(int, int, off_t);
-ssize_t splice(int, off_t, int, off_t, size_t, unsigned int);
 #endif
 
 #if defined(_GNU_SOURCE)
+ssize_t splice(int, off_t, int, off_t, size_t, unsigned int);
 #define F_OWNER_TID 0
 #define F_OWNER_PID 1
 #define F_OWNER_PGRP 2