diff --git a/libc/include/sys/signalfd.h b/libc/include/sys/signalfd.h
index bd911f7..f669cc8 100644
--- a/libc/include/sys/signalfd.h
+++ b/libc/include/sys/signalfd.h
@@ -48,11 +48,11 @@
  *
  * Available since API level 18.
  */
-int signalfd(int __fd, const sigset_t* __mask, int __flags) __INTRODUCED_IN(18);
+int signalfd(int __fd, const sigset_t* _Nonnull __mask, int __flags) __INTRODUCED_IN(18);
 
 /**
  * Like signalfd() but allows setting a signal mask with RT signals even from a 32-bit process.
  */
-int signalfd64(int __fd, const sigset64_t* __mask, int __flags) __INTRODUCED_IN(28);
+int signalfd64(int __fd, const sigset64_t* _Nonnull __mask, int __flags) __INTRODUCED_IN(28);
 
 __END_DECLS