diff --git a/libc/include/sys/user.h b/libc/include/sys/user.h
index d63fe6a..12af664 100644
--- a/libc/include/sys/user.h
+++ b/libc/include/sys/user.h
@@ -35,6 +35,9 @@
 
 __BEGIN_DECLS
 
+#define PAGE_SIZE 4096
+#define PAGE_MASK (~(PAGE_SIZE - 1))
+
 #if __i386__
 
 struct user_fpregs_struct {