diff --git a/src/sections.zig b/src/sections.zig
index fa18182..b3b710c 100644
--- a/src/sections.zig
+++ b/src/sections.zig
@@ -344,12 +344,15 @@ pub fn groupsSection(
     };
 }
 
-// creates a bdz index using packed_mphf. buf[bdz_search(key)] = index(keys, key)
+// creates a bdz index using packed_mphf.
+//   hash = bdz_search(packed_mphf, keys[i]);
+//   result[hash] = idx2offset[i];
 pub fn bdzIdx(
     comptime T: type,
     allocator: Allocator,
     packed_mphf: []const u8,
     keys: []const T,
+    idx2offset: []const u32,
 ) error{OutOfMemory}![]const u32 {
     const search_fn = comptime blk: {
         switch (T) {
@@ -361,7 +364,7 @@ pub fn bdzIdx(
     assert(keys.len <= math.maxInt(u32));
     var result = try allocator.alloc(u32, keys.len);
     for (keys) |key, i|
-        result[search_fn(packed_mphf, key)] = @intCast(u32, i);
+        result[search_fn(packed_mphf, key)] = idx2offset[i];
     return result;
 }
 
@@ -441,17 +444,16 @@ pub const AllSections = struct {
         var groups = try groupsSection(allocator, corpus, group_members.idx2offset);
         errdefer groups.deinit(allocator);
 
-        // TODO: these indices must point to the *offsets*, not the indices in "users"
-        var idx_gid2group = try bdzIdx(u32, allocator, bdz_gid, gids);
+        var idx_gid2group = try bdzIdx(u32, allocator, bdz_gid, gids, groups.idx2offset);
         errdefer allocator.free(idx_gid2group);
 
-        var idx_groupname2group = try bdzIdx([]const u8, allocator, bdz_groupname, gnames);
+        var idx_groupname2group = try bdzIdx([]const u8, allocator, bdz_groupname, gnames, groups.idx2offset);
         errdefer allocator.free(idx_groupname2group);
 
-        var idx_uid2user = try bdzIdx(u32, allocator, bdz_uid, uids);
+        var idx_uid2user = try bdzIdx(u32, allocator, bdz_uid, uids, users.idx2offset);
         errdefer allocator.free(idx_uid2user);
 
-        var idx_name2user = try bdzIdx([]const u8, allocator, bdz_username, unames);
+        var idx_name2user = try bdzIdx([]const u8, allocator, bdz_username, unames, users.idx2offset);
         errdefer allocator.free(idx_name2user);
 
         return AllSections{
@@ -694,21 +696,23 @@ test "users compare function" {
     try testing.expect(!cmpUser({}, bb, b));
 }
 
+const hash_offsets = &[_]u32{ 0, 10, 20, 30 };
+
 fn expectUsedHashes(allocator: Allocator, arr: []const u32) !void {
-    var used = try allocator.alloc(bool, arr.len);
-    defer allocator.free(used);
-    mem.set(bool, used, false);
+    var used = AutoHashMap(u32, void).init(allocator);
+    defer used.deinit();
+
     for (arr) |elem|
-        used[arr[elem]] = true;
-    for (used) |item|
-        try testing.expect(item);
+        try used.putNoClobber(elem, {});
+    for (hash_offsets) |item|
+        try testing.expect(used.get(item) != null);
 }
 
 test "bdzIdx on u32" {
     const keys = [_]u32{ 42, 1, 2, 3 };
     const mphf = try cmph.packU32(testing.allocator, keys[0..]);
     defer testing.allocator.free(mphf);
-    var result = try bdzIdx(u32, testing.allocator, mphf, keys[0..]);
+    var result = try bdzIdx(u32, testing.allocator, mphf, keys[0..], hash_offsets);
     defer testing.allocator.free(result);
     try expectUsedHashes(testing.allocator, result);
 }
@@ -717,7 +721,7 @@ test "bdzIdx on str" {
     const keys = [_][]const u8{ "42", "1", "2", "3" };
     const mphf = try cmph.packStr(testing.allocator, keys[0..]);
     defer testing.allocator.free(mphf);
-    var result = try bdzIdx([]const u8, testing.allocator, mphf, keys[0..]);
+    var result = try bdzIdx([]const u8, testing.allocator, mphf, keys[0..], hash_offsets);
     defer testing.allocator.free(result);
     try expectUsedHashes(testing.allocator, result);
 }