diff --git a/libc/unistd/sigsetmask.c b/libc/unistd/sigsetmask.c
index b987595..4f46458 100644
--- a/libc/unistd/sigsetmask.c
+++ b/libc/unistd/sigsetmask.c
@@ -38,6 +38,8 @@
         sigset_t  the_sigset;
     } in, out;
 
+    in.the_mask = mask;
+
     n = sigprocmask(SIG_SETMASK, &in.the_sigset, &out.the_sigset);
     if (n)
         return n;