diff --git a/src/sections.zig b/src/sections.zig
index eb59819..3a3d55a 100644
--- a/src/sections.zig
+++ b/src/sections.zig
@@ -3,6 +3,7 @@ const fmt = std.fmt;
 const mem = std.mem;
 const math = std.math;
 const sort = std.sort;
+const assert = std.debug.assert;
 const unicode = std.unicode;
 const Allocator = std.mem.Allocator;
 const ArrayListUnmanaged = std.ArrayListUnmanaged;
@@ -224,11 +225,11 @@ pub fn usersSection(
     errdefer blob.deinit();
     var i: usize = 0;
     while (i < corpus.users.len) : (i += 1) {
-        // TODO: this is inefficient; it's calling `.slice()` on every iteration
+        // TODO: this is inefficient by calling `.slice()` on every iteration
         const user = corpus.users.get(i);
-        const user_offset = try math.cast(u32, blob.items.len);
-        std.debug.assert(user_offset & 7 == 0);
-        idx2offset[i] = user_offset;
+        const user_offset = try math.cast(u35, blob.items.len);
+        assert(user_offset & 7 == 0);
+        idx2offset[i] = @truncate(u32, user_offset >> 3);
         try userImport.PackedUser.packTo(
             &blob,
             user,
@@ -324,7 +325,7 @@ pub fn groupsSection(
         // TODO: this is inefficient; it's calling `.slice()` on every iteration
         const group = corpus.groups.get(i);
         const group_offset = try math.cast(u32, blob.items.len);
-        std.debug.assert(group_offset & 7 == 0);
+        assert(group_offset & 7 == 0);
         idx2offset[i] = group_offset;
         const group_stored = groupImport.GroupStored{
             .gid = group.gid,
@@ -355,7 +356,7 @@ pub fn bdzIdx(
             else => unreachable,
         }
     };
-    std.debug.assert(keys.len <= math.maxInt(u32));
+    assert(keys.len <= math.maxInt(u32));
     var result = try allocator.alloc(u32, keys.len);
     for (keys) |key, i| {
         const hash = search_fn(packed_mphf, key);
diff --git a/src/shell.zig b/src/shell.zig
index ecdc116..ec1c09e 100644
--- a/src/shell.zig
+++ b/src/shell.zig
@@ -79,6 +79,7 @@ pub const ShellWriter = struct {
                 try self.blob.appendSlice(shells.get(idx));
                 const our_shell = self.blob.constSlice()[full_offset .. full_offset + len];
                 try self.indices.put(our_shell, idx);
+                std.debug.assert(full_offset & 3 == 0);
                 self.index.set(idx, ShellIndex{
                     .offset = try std.math.cast(u10, full_offset >> 2),
                     .len = len - 1,