diff --git a/ApplicationCommands/BirthdayModule.cs b/ApplicationCommands/BirthdayModule.cs
index 6434d8e..fec2ac0 100644
--- a/ApplicationCommands/BirthdayModule.cs
+++ b/ApplicationCommands/BirthdayModule.cs
@@ -20,7 +20,7 @@ public class BirthdayModule : BotModuleBase {
     public class SubCmdsBirthdaySet : BotModuleBase {
         [SlashCommand("date", HelpCmdSetDate)]
         public async Task CmdSetBday([Summary(description: HelpOptDate)] string date,
-                                     [Summary(description: HelpOptZone)] string? zone = null) {
+                                     [Summary(description: HelpOptZone), Autocomplete<TzAutocompleteHandler>] string? zone = null) {
             int inmonth, inday;
             try {
                 (inmonth, inday) = ParseDate(date);
@@ -63,7 +63,7 @@ public class BirthdayModule : BotModuleBase {
         }
 
         [SlashCommand("timezone", HelpCmdSetZone)]
-        public async Task CmdSetZone([Summary(description: HelpOptZone)] string zone) {
+        public async Task CmdSetZone([Summary(description: HelpOptZone), Autocomplete<TzAutocompleteHandler>] string zone) {
             using var db = new BotDatabaseContext();
 
             var user = ((SocketGuildUser)Context.User).GetUserEntryOrNew(db);
diff --git a/ApplicationCommands/BirthdayOverrideModule.cs b/ApplicationCommands/BirthdayOverrideModule.cs
index c261f94..d89c60b 100644
--- a/ApplicationCommands/BirthdayOverrideModule.cs
+++ b/ApplicationCommands/BirthdayOverrideModule.cs
@@ -44,7 +44,7 @@ public class BirthdayOverrideModule : BotModuleBase {
 
     [SlashCommand("set-timezone", "Set a user's time zone on their behalf.")]
     public async Task OvSetTimezone([Summary(description: HelpOptOvTarget)] SocketGuildUser target,
-                                    [Summary(description: HelpOptZone)] string zone) {
+                                    [Summary(description: HelpOptZone), Autocomplete<TzAutocompleteHandler>] string zone) {
         using var db = new BotDatabaseContext();
 
         var user = target.GetUserEntryOrNew(db);
diff --git a/ApplicationCommands/ConfigModule.cs b/ApplicationCommands/ConfigModule.cs
index 81c55a1..2c730b0 100644
--- a/ApplicationCommands/ConfigModule.cs
+++ b/ApplicationCommands/ConfigModule.cs
@@ -193,7 +193,7 @@ public class ConfigModule : BotModuleBase {
     }
 
     [SlashCommand("set-timezone", "Configure the time zone to use by default in the server." + HelpPofxBlankUnset)]
-    public async Task CmdSetTimezone([Summary(description: HelpOptZone)] string? zone = null) {
+    public async Task CmdSetTimezone([Summary(description: HelpOptZone), Autocomplete<TzAutocompleteHandler>] string? zone = null) {
         const string Response = ":white_check_mark: The server's time zone has been ";
 
         if (zone == null) {
diff --git a/ApplicationCommands/TzAutocompleteHandler.cs b/ApplicationCommands/TzAutocompleteHandler.cs
new file mode 100644
index 0000000..dd016b4
--- /dev/null
+++ b/ApplicationCommands/TzAutocompleteHandler.cs
@@ -0,0 +1,34 @@
+
+using BirthdayBot.Data;
+using Discord.Interactions;
+using Microsoft.EntityFrameworkCore;
+
+namespace BirthdayBot.ApplicationCommands;
+
+public class TzAutocompleteHandler : AutocompleteHandler {
+    public override Task<AutocompletionResult> GenerateSuggestionsAsync(IInteractionContext cx,
+                                                                        IAutocompleteInteraction ia, IParameterInfo pm,
+                                                                        IServiceProvider sv) {
+        var input = ((SocketAutocompleteInteraction)ia).Data.Current.Value.ToString()!;
+        var inparts = input.Split('/', 2, StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
+
+        var db = new BotDatabaseContext();
+        var query = db.UserEntries.AsNoTracking();
+        if (inparts.Length == 2) {
+            query = query.Where(u => EF.Functions.ILike(u.TimeZone!, $"%{inparts[0]}%/%{inparts[1]}%"));
+        } else {
+            // No '/' in query - search for string within each side of zone name (tested to not give conflicting results)
+            query = query.Where(u =>
+                EF.Functions.ILike(u.TimeZone!, $"%{input}%/%") || EF.Functions.ILike(u.TimeZone!, $"%/%{input}%"));
+        }
+        // TODO Could find a way to include all remaining zones at the bottom of results for full completion
+        // TODO Filter out undesirable zone names, aliases, etc from autocompletion
+        var result = query.GroupBy(u => u.TimeZone)
+            .Select(g => new { ZoneName = g.Key, Count = g.Count() })
+            .OrderByDescending(x => x.Count)
+            .Take(25)
+            .Select(x => new AutocompleteResult(x.ZoneName, x.ZoneName))
+            .ToList();
+        return Task.FromResult(AutocompletionResult.FromSuccess(result));
+    }
+}
\ No newline at end of file
diff --git a/BirthdayBot.csproj b/BirthdayBot.csproj
index 34b1e37..b5ecd18 100644
--- a/BirthdayBot.csproj
+++ b/BirthdayBot.csproj
@@ -24,7 +24,7 @@
 
   <ItemGroup>
     <PackageReference Include="CommandLineParser" Version="2.9.1" />
-    <PackageReference Include="Discord.Net" Version="3.14.1" />
+    <PackageReference Include="Discord.Net" Version="3.15.2" />
     <PackageReference Include="EFCore.NamingConventions" Version="8.0.3" />
     <PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="8.0.4">
       <PrivateAssets>all</PrivateAssets>