diff --git a/src/user.zig b/src/user.zig
index 91f6b70..ca9dd60 100644
--- a/src/user.zig
+++ b/src/user.zig
@@ -2,10 +2,8 @@ const std = @import("std");
 const pad = @import("padding.zig");
 
 const assert = std.debug.assert;
-const Allocator = std.mem.Allocator;
-const ArrayList = std.ArrayList;
-const math = std.math;
 const mem = std.mem;
+const Allocator = mem.Allocator;
 
 // ShellIndexFn is a function prototype that, given a shell's index (in
 // global shell section), will return a shell string. Matches ShelReader.get.
@@ -24,7 +22,7 @@ pub const User = struct {
 
 pub const PackedUser = struct {
     const AlignmentBits = 3;
-    const shellIndexFnType = fn ([]const u8) ?u6;
+    const shellIndexFn = fn ([]const u8) ?u6;
 
     const InnerSize = @divExact(@bitSizeOf(Inner), 8);
     const Inner = packed struct {
@@ -125,7 +123,8 @@ pub const PackedUser = struct {
         };
     }
 
-    fn downCast(comptime T: type, n: u64) error{InvalidRecord}!T {
+    pub const errInvalid = error{InvalidRecord};
+    fn downCast(comptime T: type, n: u64) errInvalid!T {
         return std.math.cast(T, n) catch |err| switch (err) {
             error.Overflow => {
                 return error.InvalidRecord;
@@ -133,7 +132,7 @@ pub const PackedUser = struct {
         };
     }
 
-    fn validateUtf8(s: []const u8) error{InvalidRecord}!void {
+    fn validateUtf8(s: []const u8) errInvalid!void {
         if (!std.unicode.utf8ValidateSlice(s)) {
             return error.InvalidRecord;
         }
@@ -142,11 +141,7 @@ 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.
     // The slice is passed as a pointer, so it can be mutated.
-    pub fn packTo(
-        buf: *[]u8,
-        user: User,
-        shellIndexFn: shellIndexFnType,
-    ) error{InvalidRecord}!void {
+    pub fn packTo(buf: *[]u8, user: User, idxFn: shellIndexFn) errInvalid!void {
         // function arguments are consts. We need to mutate the underlying
         // slice, so passing it via pointer instead.
         const home_len = try downCast(u6, user.home.len - 1);
@@ -163,10 +158,10 @@ pub const PackedUser = struct {
             .uid = user.uid,
             .gid = user.gid,
             .additional_gids_offset = std.math.maxInt(u29),
-            .shell_here = shellIndexFn(user.shell) == null,
-            .shell_len_or_idx = shellIndexFn(user.shell) orelse shell_len,
+            .shell_here = idxFn(user.shell) == null,
+            .shell_len_or_idx = idxFn(user.shell) orelse shell_len,
             .home_len = home_len,
-            .name_is_a_suffix = std.mem.endsWith(u8, user.home, user.name),
+            .name_is_a_suffix = mem.endsWith(u8, user.home, user.name),
             .name_len = name_len,
             .gecos_len = gecos_len,
         };
@@ -272,6 +267,7 @@ pub const Iterator = struct {
 };
 
 const testing = std.testing;
+const ArrayList = std.ArrayList;
 
 test "PackedUser internal and external alignment" {
     // External padding (AlignmentBits) must be higher or equal to
@@ -284,9 +280,9 @@ test "PackedUser internal and external alignment" {
 }
 
 fn testShellIndex(shell: []const u8) ?u6 {
-    if (std.mem.eql(u8, shell, "/bin/bash")) {
+    if (mem.eql(u8, shell, "/bin/bash")) {
         return 0;
-    } else if (std.mem.eql(u8, shell, "/bin/zsh")) {
+    } else if (mem.eql(u8, shell, "/bin/zsh")) {
         return 1;
     }
     return null;
@@ -320,7 +316,7 @@ test "construct PackedUser section" {
         .shell = "/usr/bin/nologin",
     }, User{
         .uid = 0,
-        .gid = math.maxInt(u32),
+        .gid = std.math.maxInt(u32),
         .name = "Name" ** 8,
         .gecos = "Gecos" ** 51,
         .home = "Home" ** 16,
@@ -352,12 +348,14 @@ test "construct PackedUser section" {
 }
 
 test "PackedUser.maxSize()" {
+    // TODO(motiejus) try using a slice that points to an array in stack.
+    // As of writing, I am getting a stack smashing error.
     var buf = try ArrayList(u8).initCapacity(testing.allocator, PackedUser.maxSize());
     defer buf.deinit();
 
     const largeUser = User{
-        .uid = math.maxInt(u32),
-        .gid = math.maxInt(u32),
+        .uid = std.math.maxInt(u32),
+        .gid = std.math.maxInt(u32),
         .name = "Name" ** 8, // 32
         .gecos = "Gecos" ** 51, // 255
         .home = "Home" ** 16, // 64