diff --git a/libc/bionic/posix_timers.cpp b/libc/bionic/posix_timers.cpp
index 1abeb1f..47d6db0 100644
--- a/libc/bionic/posix_timers.cpp
+++ b/libc/bionic/posix_timers.cpp
@@ -154,7 +154,7 @@
 
   int rc = pthread_create(&timer->callback_thread, &thread_attributes, __timer_thread_start, timer);
 
-  __rt_sigprocmask(SIG_BLOCK, &old_sigset, nullptr, sizeof(old_sigset));
+  __rt_sigprocmask(SIG_SETMASK, &old_sigset, nullptr, sizeof(old_sigset));
 
   if (rc != 0) {
     free(timer);