diff --git a/libc/bionic/sigaction.cpp b/libc/bionic/sigaction.cpp
index 42dcccd..96e6f3c 100644
--- a/libc/bionic/sigaction.cpp
+++ b/libc/bionic/sigaction.cpp
@@ -43,7 +43,8 @@
   if (bionic_new_action != nullptr) {
     kernel_new_action.sa_flags = bionic_new_action->sa_flags;
     kernel_new_action.sa_handler = bionic_new_action->sa_handler;
-    kernel_new_action.sa_mask = filter_reserved_signals(bionic_new_action->sa_mask, SIG_SETMASK);
+    // Don't filter signals here; if the caller asked for everything to be blocked, we should obey.
+    kernel_new_action.sa_mask = bionic_new_action->sa_mask;
 #if defined(SA_RESTORER)
     kernel_new_action.sa_restorer = bionic_new_action->sa_restorer;
 #if defined(__aarch64__)
@@ -95,6 +96,7 @@
 #if defined(SA_RESTORER)
     kernel_new.sa_restorer = bionic_new->sa_restorer;
 #endif
+    // Don't filter signals here; if the caller asked for everything to be blocked, we should obey.
     memcpy(&kernel_new.sa_mask, &bionic_new->sa_mask, sizeof(bionic_new->sa_mask));
   }
 
@@ -122,7 +124,8 @@
       kernel_new.sa_restorer = (kernel_new.sa_flags & SA_SIGINFO) ? &__restore_rt : &__restore;
     }
 #endif
-    kernel_new.sa_mask = filter_reserved_signals(kernel_new.sa_mask, SIG_SETMASK);
+    // Don't filter signals here; if the caller asked for everything to be blocked, we should obey.
+    kernel_new.sa_mask = kernel_new.sa_mask;
   }
 
   return __rt_sigaction(signal,
diff --git a/tests/signal_test.cpp b/tests/signal_test.cpp
index dd27aef..77b004f 100644
--- a/tests/signal_test.cpp
+++ b/tests/signal_test.cpp
@@ -392,11 +392,19 @@
   static uint64_t sigset;
   struct sigaction sa = {};
   sa.sa_handler = [](int) { sigset = GetSignalMask(); };
+  sa.sa_flags = SA_ONSTACK | SA_NODEFER;
   sigfillset(&sa.sa_mask);
   sigaction(SIGUSR1, &sa, nullptr);
   raise(SIGUSR1);
-  ASSERT_NE(0ULL, sigset);
-  TestSignalMaskFiltered(sigset);
+
+  // On LP32, struct sigaction::sa_mask is only 32-bits wide.
+  unsigned long expected_sigset = ~0UL;
+
+  // SIGKILL and SIGSTOP are always blocked.
+  expected_sigset &= ~(1UL << (SIGKILL - 1));
+  expected_sigset &= ~(1UL << (SIGSTOP - 1));
+
+  ASSERT_EQ(static_cast<uint64_t>(expected_sigset), sigset);
 }
 
 TEST(signal, sigaction64_filter) {
@@ -404,11 +412,18 @@
   static uint64_t sigset;
   struct sigaction64 sa = {};
   sa.sa_handler = [](int) { sigset = GetSignalMask(); };
+  sa.sa_flags = SA_ONSTACK | SA_NODEFER;
   sigfillset64(&sa.sa_mask);
   sigaction64(SIGUSR1, &sa, nullptr);
   raise(SIGUSR1);
-  ASSERT_NE(0ULL, sigset);
-  TestSignalMaskFiltered(sigset);
+
+  uint64_t expected_sigset = ~0ULL;
+
+  // SIGKILL and SIGSTOP are always blocked.
+  expected_sigset &= ~(1ULL << (SIGKILL - 1));
+  expected_sigset &= ~(1ULL << (SIGSTOP - 1));
+
+  ASSERT_EQ(expected_sigset, sigset);
 }
 
 TEST(signal, sigprocmask_setmask_filter) {