diff --git a/libc/bionic/pthread_create.cpp b/libc/bionic/pthread_create.cpp
index 0dbf539..1dc1066 100644
--- a/libc/bionic/pthread_create.cpp
+++ b/libc/bionic/pthread_create.cpp
@@ -344,6 +344,8 @@
         name);
 }
 
+extern "C" int __rt_sigprocmask(int, const sigset64_t*, sigset64_t*, size_t);
+
 __attribute__((no_sanitize("hwaddress")))
 static int __pthread_start(void* arg) {
   pthread_internal_t* thread = reinterpret_cast<pthread_internal_t*>(arg);
@@ -358,6 +360,7 @@
 
   __set_stack_and_tls_vma_name(false);
   __init_additional_stacks(thread);
+  __rt_sigprocmask(SIG_SETMASK, &thread->start_mask, nullptr, sizeof(thread->start_mask));
 
   void* result = thread->start_routine(thread->start_routine_arg);
   pthread_exit(result);
@@ -420,7 +423,12 @@
   __init_user_desc(&tls_descriptor, false, tls);
   tls = &tls_descriptor;
 #endif
+
+  sigset64_t block_all_mask;
+  sigfillset64(&block_all_mask);
+  __rt_sigprocmask(SIG_SETMASK, &block_all_mask, &thread->start_mask, sizeof(thread->start_mask));
   int rc = clone(__pthread_start, child_stack, flags, thread, &(thread->tid), tls, &(thread->tid));
+  __rt_sigprocmask(SIG_SETMASK, &thread->start_mask, nullptr, sizeof(thread->start_mask));
   if (rc == -1) {
     int clone_errno = errno;
     // We don't have to unlock the mutex at all because clone(2) failed so there's no child waiting to
diff --git a/libc/bionic/pthread_internal.h b/libc/bionic/pthread_internal.h
index 22cc400..22b0558 100644
--- a/libc/bionic/pthread_internal.h
+++ b/libc/bionic/pthread_internal.h
@@ -98,6 +98,7 @@
   void* (*start_routine)(void*);
   void* start_routine_arg;
   void* return_value;
+  sigset64_t start_mask;
 
   void* alternate_signal_stack;