4 files changed, 24 insertions, 18 deletions
diff --git a/lib/std/Thread.zig b/lib/std/Thread.zig
index b9a69d151f..7e8a6226e6 100644
--- a/lib/std/Thread.zig
+++ b/lib/std/Thread.zig
@@ -362,7 +362,7 @@ pub fn spawn(comptime startFn: anytype, context: SpawnContextType(@TypeOf(startF
             os.EAGAIN => return error.SystemResources,
             os.EPERM => unreachable,
             os.EINVAL => unreachable,
-            else => return os.unexpectedErrno(@intCast(usize, err)),
+            else => return os.unexpectedErrno(err),
         }
 
         return thread_obj;
diff --git a/lib/std/c.zig b/lib/std/c.zig
index 1688824dd9..bd0ce04f75 100644
--- a/lib/std/c.zig
+++ b/lib/std/c.zig
@@ -37,9 +37,9 @@ pub usingnamespace switch (std.Target.current.os.tag) {
     else => struct {},
 };
 
-pub fn getErrno(rc: anytype) u16 {
+pub fn getErrno(rc: anytype) c_int {
     if (rc == -1) {
-        return @intCast(u16, _errno().*);
+        return _errno().*;
     } else {
         return 0;
     }
diff --git a/lib/std/io/c_writer.zig b/lib/std/io/c_writer.zig
index fa7d7eb13a..26ae1fde01 100644
--- a/lib/std/io/c_writer.zig
+++ b/lib/std/io/c_writer.zig
@@ -30,7 +30,7 @@ fn cWriterWrite(c_file: *std.c.FILE, bytes: []const u8) std.fs.File.WriteError!u
         os.ENOSPC => return error.NoSpaceLeft,
         os.EPERM => return error.AccessDenied,
         os.EPIPE => return error.BrokenPipe,
-        else => |err| return os.unexpectedErrno(@intCast(usize, err)),
+        else => |err| return os.unexpectedErrno(err),
     }
 }
 
diff --git a/lib/std/os.zig b/lib/std/os.zig
index a2e62ed0ae..362a58f7fb 100644
--- a/lib/std/os.zig
+++ b/lib/std/os.zig
@@ -144,25 +144,27 @@ pub fn getrandom(buffer: []u8) GetRandomError!void {
             std.c.versionCheck(builtin.Version{ .major = 2, .minor = 25, .patch = 0 }).ok;
 
         while (buf.len != 0) {
-            var err: u16 = undefined;
-
-            const num_read = if (use_c) blk: {
+            const res = if (use_c) blk: {
                 const rc = std.c.getrandom(buf.ptr, buf.len, 0);
-                err = std.c.getErrno(rc);
-                break :blk @bitCast(usize, rc);
+                break :blk .{
+                    .num_read = @bitCast(usize, rc),
+                    .err = std.c.getErrno(rc),
+                };
             } else blk: {
                 const rc = linux.getrandom(buf.ptr, buf.len, 0);
-                err = linux.getErrno(rc);
-                break :blk rc;
+                break :blk .{
+                    .num_read = rc,
+                    .err = linux.getErrno(rc),
+                };
             };
 
-            switch (err) {
-                0 => buf = buf[num_read..],
+            switch (res.err) {
+                0 => buf = buf[res.num_read..],
                 EINVAL => unreachable,
                 EFAULT => unreachable,
                 EINTR => continue,
                 ENOSYS => return getRandomBytesDevURandom(buf),
-                else => return unexpectedErrno(err),
+                else => return unexpectedErrno(res.err),
             }
         }
         return;
@@ -1500,7 +1502,7 @@ pub fn getcwd(out_buffer: []u8) GetCwdError![]u8 {
         EINVAL => unreachable,
         ENOENT => return error.CurrentWorkingDirectoryUnlinked,
         ERANGE => return error.NameTooLong,
-        else => return unexpectedErrno(@intCast(usize, err)),
+        else => return unexpectedErrno(err),
     }
 }
 
@@ -3661,7 +3663,7 @@ pub fn mmap(
     const err = if (builtin.link_libc) blk: {
         const rc = std.c.mmap(ptr, length, prot, flags, fd, offset);
         if (rc != std.c.MAP_FAILED) return @ptrCast([*]align(mem.page_size) u8, @alignCast(mem.page_size, rc))[0..length];
-        break :blk @intCast(usize, system._errno().*);
+        break :blk system._errno().*;
     } else blk: {
         const rc = system.mmap(ptr, length, prot, flags, fd, offset);
         const err = errno(rc);
@@ -4321,7 +4323,7 @@ pub fn realpathZ(pathname: [*:0]const u8, out_buffer: *[MAX_PATH_BYTES]u8) RealP
         ENAMETOOLONG => return error.NameTooLong,
         ELOOP => return error.SymLinkLoop,
         EIO => return error.InputOutput,
-        else => |err| return unexpectedErrno(@intCast(usize, err)),
+        else => |err| return unexpectedErrno(err),
     };
     return mem.spanZ(result_path);
 }
@@ -4622,7 +4624,11 @@ pub const UnexpectedError = error{
 
 /// Call this when you made a syscall or something that sets errno
 /// and you get an unexpected error.
-pub fn unexpectedErrno(err: usize) UnexpectedError {
+pub fn unexpectedErrno(err: anytype) UnexpectedError {
+    if (@typeInfo(@TypeOf(err)) != .Int) {
+        @compileError("err is expected to be an integer");
+    }
+
     if (unexpected_error_tracing) {
         std.debug.warn("unexpected errno: {d}\n", .{err});
         std.debug.dumpCurrentStackTrace(null);