diff --git a/lib/std/c.zig b/lib/std/c.zig
index 6ad7d2c60a..a9c70a598e 100644
--- a/lib/std/c.zig
+++ b/lib/std/c.zig
@@ -262,6 +262,7 @@ pub extern "c" fn pthread_key_create(key: *c.pthread_key_t, destructor: ?PThread
 pub extern "c" fn pthread_key_delete(key: c.pthread_key_t) c.E;
 pub extern "c" fn pthread_getspecific(key: c.pthread_key_t) ?*anyopaque;
 pub extern "c" fn pthread_setspecific(key: c.pthread_key_t, value: ?*anyopaque) c_int;
+pub extern "c" fn pthread_sigmask(how: c_int, set: *const c.sigset_t, oldset: *c.sigset_t) c_int;
 pub extern "c" fn sem_init(sem: *c.sem_t, pshared: c_int, value: c_uint) c_int;
 pub extern "c" fn sem_destroy(sem: *c.sem_t) c_int;
 pub extern "c" fn sem_open(name: [*:0]const u8, flag: c_int, mode: c.mode_t, value: c_uint) *c.sem_t;