diff --git a/glfw/ibus_glfw.c b/glfw/ibus_glfw.c
index fd4af17c9..9e2bb1777 100644
--- a/glfw/ibus_glfw.c
+++ b/glfw/ibus_glfw.c
@@ -24,6 +24,10 @@
 //
 //========================================================================
 
+// _POSIX_C_SOURCE needed for fileno() on Linux systems
+#define _POSIX_C_SOURCE 1
+#include <stdio.h>
+#undef _POSIX_C_SOURCE
 #include <errno.h>
 #include <stdlib.h>
 #include <string.h>