diff --git a/std/c/darwin.zig b/std/c/darwin.zig
index e45a158f68d3f5e67143e1d3e36a94d78a9a9dd6..d25cd14fc42a5271438cd6d780e010bbc62ebe83 100644
--- a/std/c/darwin.zig
+++ b/std/c/darwin.zig
@@ -54,3 +54,5 @@ pub extern "c" fn mach_port_deallocate(task: ipc_space_t, name: mach_port_name_t
 pub fn sigaddset(set: *sigset_t, signo: u5) void {
     set.* |= u32(1) << (signo - 1);
 }
+
+pub extern "c" fn sigaltstack(ss: ?*stack_t, old_ss: ?*stack_t) c_int;