diff --git a/glfw/ibus_glfw.c b/glfw/ibus_glfw.c
index 7d2baa3b2..0ff14c27d 100644
--- a/glfw/ibus_glfw.c
+++ b/glfw/ibus_glfw.c
@@ -24,10 +24,8 @@
 //
 //========================================================================
 
-// _POSIX_C_SOURCE needed for fileno() on Linux systems
-#define _POSIX_C_SOURCE 1
+#define _GNU_SOURCE
 #include <stdio.h>
-#undef _POSIX_C_SOURCE
 #include <errno.h>
 #include <stdlib.h>
 #include <string.h>