diff --git a/lib/std/os/plan9.zig b/lib/std/os/plan9.zig
index 7e047c728c2ad592c232d94634974d11f755adba..dbf33894cb254f97a6652d8f4f22d883c4b938b8 100644
--- a/lib/std/os/plan9.zig
+++ b/lib/std/os/plan9.zig
@@ -60,8 +60,8 @@ pub const SYS = enum(usize) {
     _NSEC = 53,
 };
 
-pub fn pwrite(fd: usize, buf: [*]const u8, count: usize, offset: usize) void {
-    syscall_bits.syscall4(.PWRITE, fd, @ptrToInt(buf), count, offset);
+pub fn pwrite(fd: usize, buf: [*]const u8, count: usize, offset: usize) usize {
+    return syscall_bits.syscall4(.PWRITE, fd, @ptrToInt(buf), count, offset);
 }
 
 pub fn exits(status: ?[*:0]const u8) void {
diff --git a/lib/std/os/plan9/x86_64.zig b/lib/std/os/plan9/x86_64.zig
index d24b29d0a86d40a9b618f1bc7da603fe21be9ffc..652c18edb85662312ac41c34fedce324b4c6cb4e 100644
--- a/lib/std/os/plan9/x86_64.zig
+++ b/lib/std/os/plan9/x86_64.zig
@@ -2,8 +2,8 @@ const plan9 = @import("../plan9.zig");
 // TODO get ret from inline asm
 // TODO better inline asm
 
-pub fn syscall4(sys: plan9.SYS, arg0: usize, arg1: usize, arg2: usize, arg3: usize) void {
-    asm volatile (
+pub fn syscall4(sys: plan9.SYS, arg0: usize, arg1: usize, arg2: usize, arg3: usize) usize {
+    return asm volatile (
         \\push %%r11
         \\push %%r10
         \\push %%r9
@@ -15,7 +15,8 @@ pub fn syscall4(sys: plan9.SYS, arg0: usize, arg1: usize, arg2: usize, arg3: usi
         \\pop %%r11
         \\pop %%r11
         \\pop %%r11
-        :
+        : [ret] "={rax}" (-> usize),
+          // :
         : [arg0] "{r8}" (arg0),
           [arg1] "{r9}" (arg1),
           [arg2] "{r10}" (arg2),