diff --git a/Userland/Libraries/LibC/sys/ioctl.h b/Userland/Libraries/LibC/sys/ioctl.h
index 55d4affa27..dbded83718 100644
--- a/Userland/Libraries/LibC/sys/ioctl.h
+++ b/Userland/Libraries/LibC/sys/ioctl.h
@@ -11,6 +11,8 @@
 
 __BEGIN_DECLS
 
+#define FIONREAD 0x541B
+
 int ioctl(int fd, unsigned request, ...);
 
 __END_DECLS