diff --git a/std/os/zen.zig b/std/os/zen.zig
index ffc491e404bd3fe1266496f52cb486ea81036537..37ec68763db27f41f3dbbe475a66e76f22444d93 100644
--- a/std/os/zen.zig
+++ b/std/os/zen.zig
@@ -9,16 +9,23 @@ pub const MBOX_TERMINAL = 1;
 ////  Syscall numbers  ////
 ///////////////////////////
 
-pub const SYS_createMailbox = 0;
-pub const SYS_send = 1;
-pub const SYS_receive = 2;
-pub const SYS_map = 3;
+pub const SYS_exit = 0;
+pub const SYS_createMailbox = 1;
+pub const SYS_send = 2;
+pub const SYS_receive = 3;
+pub const SYS_map = 4;
+pub const SYS_createThread = 5;
 
 
 ////////////////////
 ////  Syscalls  ////
 ////////////////////
 
+pub fn exit(status: i32) -> noreturn {
+    _ = syscall1(SYS_exit, @bitCast(usize, isize(status)));
+    unreachable;
+}
+
 pub fn createMailbox(id: u16) {
     _ = syscall1(SYS_createMailbox, id);
 }
@@ -35,6 +42,10 @@ pub fn map(v_addr: usize, p_addr: usize, size: usize, writable: bool) -> bool {
     return syscall4(SYS_map, v_addr, p_addr, size, usize(writable)) != 0;
 }
 
+pub fn createThread(function: fn()) -> u16 {
+    return u16(syscall1(SYS_createThread, @ptrToInt(function)));
+}
+
 
 /////////////////////////
 ////  Syscall stubs  ////
diff --git a/std/special/bootstrap.zig b/std/special/bootstrap.zig
index 28175de725fd78184088e505ff5a8b6a96590e19..55d28a2d0e07ab511a63e3c2876ad8a92d5a04ad 100644
--- a/std/special/bootstrap.zig
+++ b/std/special/bootstrap.zig
@@ -21,9 +21,8 @@ comptime {
 }
 
 extern fn zenMain() -> noreturn {
-    // TODO: call exit.
-    root.main() catch {};
-    while (true) {}
+    root.main() catch std.os.posix.exit(1);
+    std.os.posix.exit(0);
 }
 
 nakedcc fn _start() -> noreturn {