diff --git a/libc/include/bits/setjmp-types.h b/libc/include/bits/setjmp-types.h
index 439f7a38..386fb876 100644
--- a/libc/include/bits/setjmp-types.h
+++ b/libc/include/bits/setjmp-types.h
@@ -5,6 +5,7 @@
 
 #include <bits/fixed-size-types.h>
 #include <bits/platform.h>
+#include <bits/signal.h>
 
 #ifndef _SETJMP_H
 #error "Never use bits/setjmp-types.h directly; include setjmp.h instead."
@@ -12,7 +13,13 @@
 
 #ifdef __libc_arch_x86_64
 typedef __u64_t jmp_buf[8];
-typedef __u64_t sigjmp_buf[8];
+typedef struct
+{
+    jmp_buf buf;
+    sigset_t set;
+    int saved;
+} __sigjmp_buf_tag;
+typedef __sigjmp_buf_tag sigjmp_buf[1];
 #else
 #error "Unsupported architecture."
 #endif
diff --git a/libc/include/setjmp.h b/libc/include/setjmp.h
index 9538c94f..c1fe3584 100644
--- a/libc/include/setjmp.h
+++ b/libc/include/setjmp.h
@@ -14,13 +14,13 @@ extern "C"
     /* Saves the current execution state in env. */
     int setjmp(jmp_buf env);
 
-    /* Right now, does the exact same thing as setjmp() (savesigs is ignored), since signals are not implemented. */
+    /* Saves the current execution state (and optionally, the current signal mask) in env. */
     int sigsetjmp(sigjmp_buf env, int savesigs);
 
     /* Restores the execution state saved in env by a setjmp() call. */
     __noreturn void longjmp(jmp_buf env, int val);
 
-    /* Right now, does the exact same as longjmp(), since signals are not implemented. */
+    /* Restores the execution state saved in env by a sigsetjmp() call. */
     __noreturn void siglongjmp(sigjmp_buf env, int val);
 
 #ifdef __cplusplus
diff --git a/libc/src/setjmp.cpp b/libc/src/setjmp.cpp
index 2d2bf673..932a0694 100644
--- a/libc/src/setjmp.cpp
+++ b/libc/src/setjmp.cpp
@@ -1,14 +1,17 @@
 #include <setjmp.h>
+#include <signal.h>
 
 extern "C"
 {
-    int sigsetjmp(sigjmp_buf env, int)
+    int sigsetjmp(sigjmp_buf env, int savesigs)
     {
-        return setjmp(env);
+        if (savesigs) env->saved = 1, sigprocmask(0, nullptr, &env->set);
+        return setjmp(env->buf);
     }
 
     __noreturn void siglongjmp(sigjmp_buf env, int val)
     {
-        longjmp(env, val);
+        if (env->saved) sigprocmask(SIG_SETMASK, &env->set, nullptr);
+        longjmp(env->buf, val);
     }
 }