diff --git a/libc/arch-x86_64/bionic/setjmp.S b/libc/arch-x86_64/bionic/setjmp.S
index a8f614f..28981fa 100644
--- a/libc/arch-x86_64/bionic/setjmp.S
+++ b/libc/arch-x86_64/bionic/setjmp.S
@@ -48,6 +48,7 @@
 #define _JB_PC 7
 #define _JB_SIGFLAG 8
 #define _JB_SIGMASK 9
+#define _JB_SIGMASK_RT 10 // sigprocmask will write here too.
 
 ENTRY(setjmp)
   movl $1,%esi
@@ -62,18 +63,19 @@
 // int sigsetjmp(sigjmp_buf env, int save_signal_mask);
 ENTRY(sigsetjmp)
   // Record whether or not we're saving the signal mask.
-  movl %esi,(_JB_SIGFLAG  * 8)(%rdi)
+  movl %esi,(_JB_SIGFLAG * 8)(%rdi)
 
   // Do we need to save the signal mask?
   testl %esi,%esi
   jz 2f
 
-  // Save the signal mask.
-  pushq %rdi
-  xorq %rdi,%rdi
-  call PIC_PLT(sigblock)
-  popq %rdi
-  movq %rax,(_JB_SIGMASK * 8)(%rdi)
+  // Save current signal mask.
+  pushq %rdi // Push 'env'.
+  // The 'how' argument is ignored if new_mask is NULL.
+  xorq %rsi,%rsi // NULL.
+  leaq (_JB_SIGMASK * 8)(%rdi),%rdx // old_mask.
+  call PIC_PLT(sigprocmask)
+  popq %rdi // Pop 'env'.
 
 2:
   // Save the callee-save registers.
@@ -97,12 +99,14 @@
   pushq %rsi // Push 'value'.
 
   // Do we need to restore the signal mask?
-  cmpl $0, (_JB_SIGFLAG * 8)(%rdi)
+  cmpl $0,(_JB_SIGFLAG * 8)(%rdi)
   jz 2f
 
   // Restore the signal mask.
-  movq (_JB_SIGMASK * 8)(%rdi),%rdi
-  call PIC_PLT(sigsetmask)
+  movq $2,%rdi // SIG_SETMASK.
+  leaq (_JB_SIGMASK * 8)(%r12),%rsi // new_mask.
+  xorq %rdx,%rdx // NULL.
+  call PIC_PLT(sigprocmask)
 
 2:
   popq %rax // Pop 'value'.
diff --git a/tests/setjmp_test.cpp b/tests/setjmp_test.cpp
index 2df0135..2ea01b3 100644
--- a/tests/setjmp_test.cpp
+++ b/tests/setjmp_test.cpp
@@ -63,17 +63,29 @@
   }
 }
 
-static sigset_t SigSetOf(int signal) {
+static sigset_t SigSetOf(int signal, int rt_signal = 0) {
   sigset_t ss;
   sigemptyset(&ss);
   sigaddset(&ss, signal);
+  if (rt_signal != 0) {
+    sigaddset(&ss, rt_signal);
+  }
   return ss;
 }
 
+void AssertSigmaskEquals(const sigset_t& expected) {
+  sigset_t actual;
+  sigprocmask(0 /* ignored */, NULL, &actual);
+  size_t end = sizeof(sigset_t) * 8;
+  for (size_t i = 1; i <= end; ++i) {
+    EXPECT_EQ(sigismember(&expected, i), sigismember(&actual, i)) << i;
+  }
+}
+
 TEST(setjmp, _setjmp_signal_mask) {
   // _setjmp/_longjmp do not save/restore the signal mask.
-  sigset_t ss1(SigSetOf(SIGUSR1));
-  sigset_t ss2(SigSetOf(SIGUSR2));
+  sigset_t ss1(SigSetOf(SIGUSR1, SIGRTMIN + 8));
+  sigset_t ss2(SigSetOf(SIGUSR2, SIGRTMIN + 9));
   sigset_t original_set;
   sigprocmask(SIG_SETMASK, &ss1, &original_set);
   jmp_buf jb;
@@ -82,9 +94,7 @@
     _longjmp(jb, 1);
     FAIL(); // Unreachable.
   } else {
-    sigset_t ss;
-    sigprocmask(SIG_SETMASK, NULL, &ss);
-    EXPECT_TRUE(sigismember(&ss, SIGUSR2));
+    AssertSigmaskEquals(ss2);
   }
   sigprocmask(SIG_SETMASK, &original_set, NULL);
 }
@@ -93,8 +103,8 @@
   // setjmp/longjmp do save/restore the signal mask on bionic, but not on glibc.
   // This is a BSD versus System V historical accident. POSIX leaves the
   // behavior unspecified, so any code that cares needs to use sigsetjmp.
-  sigset_t ss1(SigSetOf(SIGUSR1));
-  sigset_t ss2(SigSetOf(SIGUSR2));
+  sigset_t ss1(SigSetOf(SIGUSR1, SIGRTMIN + 8));
+  sigset_t ss2(SigSetOf(SIGUSR2, SIGRTMIN + 9));
   sigset_t original_set;
   sigprocmask(SIG_SETMASK, &ss1, &original_set);
   jmp_buf jb;
@@ -103,14 +113,12 @@
     longjmp(jb, 1);
     FAIL(); // Unreachable.
   } else {
-    sigset_t ss;
-    sigprocmask(SIG_SETMASK, NULL, &ss);
 #if defined(__BIONIC__)
     // bionic behaves like BSD and does save/restore the signal mask.
-    EXPECT_TRUE(sigismember(&ss, SIGUSR1));
+    AssertSigmaskEquals(ss1);
 #else
     // glibc behaves like System V and doesn't save/restore the signal mask.
-    EXPECT_TRUE(sigismember(&ss, SIGUSR2));
+    AssertSigmaskEquals(ss2);
 #endif
   }
   sigprocmask(SIG_SETMASK, &original_set, NULL);
@@ -118,8 +126,8 @@
 
 TEST(setjmp, sigsetjmp_0_signal_mask) {
   // sigsetjmp(0)/siglongjmp do not save/restore the signal mask.
-  sigset_t ss1(SigSetOf(SIGUSR1));
-  sigset_t ss2(SigSetOf(SIGUSR2));
+  sigset_t ss1(SigSetOf(SIGUSR1, SIGRTMIN + 8));
+  sigset_t ss2(SigSetOf(SIGUSR2, SIGRTMIN + 9));
   sigset_t original_set;
   sigprocmask(SIG_SETMASK, &ss1, &original_set);
   sigjmp_buf sjb;
@@ -128,17 +136,15 @@
     siglongjmp(sjb, 1);
     FAIL(); // Unreachable.
   } else {
-    sigset_t ss;
-    sigprocmask(SIG_SETMASK, NULL, &ss);
-    EXPECT_TRUE(sigismember(&ss, SIGUSR2));
+    AssertSigmaskEquals(ss2);
   }
   sigprocmask(SIG_SETMASK, &original_set, NULL);
 }
 
 TEST(setjmp, sigsetjmp_1_signal_mask) {
   // sigsetjmp(1)/siglongjmp does save/restore the signal mask.
-  sigset_t ss1(SigSetOf(SIGUSR1));
-  sigset_t ss2(SigSetOf(SIGUSR2));
+  sigset_t ss1(SigSetOf(SIGUSR1, SIGRTMIN + 8));
+  sigset_t ss2(SigSetOf(SIGUSR2, SIGRTMIN + 9));
   sigset_t original_set;
   sigprocmask(SIG_SETMASK, &ss1, &original_set);
   sigjmp_buf sjb;
@@ -147,9 +153,7 @@
     siglongjmp(sjb, 1);
     FAIL(); // Unreachable.
   } else {
-    sigset_t ss;
-    sigprocmask(SIG_SETMASK, NULL, &ss);
-    EXPECT_TRUE(sigismember(&ss, SIGUSR1));
+    AssertSigmaskEquals(ss1);
   }
   sigprocmask(SIG_SETMASK, &original_set, NULL);
 }