diff --git a/src/user.zig b/src/user.zig
index 692b62a..da41488 100644
--- a/src/user.zig
+++ b/src/user.zig
@@ -21,11 +21,9 @@ pub const User = struct {
 };
 
 pub const PackedUser = struct {
-    // TODO: use @bitSizeOf(Inner)/8:
-    //const InnerSize = @divExact(@bitSizeOf(Inner), 8);
     const shellIndexFnType = fn ([]const u8) ?u6;
 
-    const InnerSize = @sizeOf(Inner);
+    const InnerSize = @divExact(@bitSizeOf(Inner), 8);
     const Inner = packed struct {
         uid: u32,
         gid: u32,
@@ -96,6 +94,7 @@ pub const PackedUser = struct {
     pub fn fromBytes(bytes: []const u8) PackedUser {
         const inner = std.mem.bytesAsValue(
             PackedUser,
+            // https://github.com/ziglang/zig/issues/10958
             bytes[0..@sizeOf(Inner)][0..@sizeOf(Inner)],
         );
 
@@ -123,8 +122,10 @@ pub const PackedUser = struct {
 
     // packTo packs the User record and copies it to the given byte slice. The
     // slice must have at least maxRecordSize() bytes available.
-    pub fn packTo(buf1: *[]u8, user: User, shellIndexFn: shellIndexFnType) error{InvalidRecord}!void {
-        var buf = buf1.*;
+    pub fn packTo(bufPtr: *[]u8, user: User, shellIndexFn: shellIndexFnType) error{InvalidRecord}!void {
+        // function arguments are consts. We need to mutate the underlying
+        // slice, so passing it via pointer instead.
+        var buf = bufPtr.*;
         const bufStart = @ptrToInt(buf.ptr);
 
         const home_len = try downCast(u6, user.home.len - 1);