diff --git a/src/chat.rs b/src/chat.rs
index 548943036..bc5a1a77c 100644
--- a/src/chat.rs
+++ b/src/chat.rs
@@ -1,7 +1,7 @@
 //! # Chat module.
 
 use std::cmp;
-use std::collections::{BTreeSet, HashMap, HashSet};
+use std::collections::{BTreeSet, HashMap};
 use std::fmt;
 use std::io::Cursor;
 use std::marker::Sync;
@@ -3774,7 +3774,7 @@ pub(crate) async fn update_chat_contacts_table(
     context: &Context,
     timestamp: i64,
     id: ChatId,
-    contacts: &HashSet<ContactId>,
+    contacts: &BTreeSet<ContactId>,
 ) -> Result<()> {
     context
         .sql
@@ -5033,7 +5033,7 @@ async fn set_contacts_by_addrs(context: &Context, id: ChatId, addrs: &[String])
         chat.typ == Chattype::OutBroadcast,
         "{id} is not a broadcast list",
     );
-    let mut contacts = HashSet::new();
+    let mut contacts = BTreeSet::new();
     for addr in addrs {
         let contact_addr = ContactAddress::new(addr)?;
         let contact = Contact::add_or_lookup(context, "", &contact_addr, Origin::Hidden)
@@ -5041,7 +5041,7 @@ async fn set_contacts_by_addrs(context: &Context, id: ChatId, addrs: &[String])
             .0;
         contacts.insert(contact);
     }
-    let contacts_old = HashSet::<ContactId>::from_iter(get_chat_contacts(context, id).await?);
+    let contacts_old = BTreeSet::<ContactId>::from_iter(get_chat_contacts(context, id).await?);
     if contacts == contacts_old {
         return Ok(());
     }
diff --git a/src/message.rs b/src/message.rs
index 0ae7591cc..b5a9caf4a 100644
--- a/src/message.rs
+++ b/src/message.rs
@@ -1,7 +1,6 @@
 //! # Messages and their identifiers.
 
 use std::collections::BTreeSet;
-use std::collections::HashSet;
 use std::path::{Path, PathBuf};
 use std::str;
 
@@ -1693,7 +1692,7 @@ pub(crate) async fn delete_msg_locally(context: &Context, msg: &Message) -> Resu
 pub(crate) async fn delete_msgs_locally_done(
     context: &Context,
     msg_ids: &[MsgId],
-    modified_chat_ids: HashSet<ChatId>,
+    modified_chat_ids: BTreeSet<ChatId>,
 ) -> Result<()> {
     for modified_chat_id in modified_chat_ids {
         context.emit_msgs_changed_without_msg_id(modified_chat_id);
@@ -1723,7 +1722,7 @@ pub async fn delete_msgs_ex(
     msg_ids: &[MsgId],
     delete_for_all: bool,
 ) -> Result<()> {
-    let mut modified_chat_ids = HashSet::new();
+    let mut modified_chat_ids = BTreeSet::new();
     let mut deleted_rfc724_mid = Vec::new();
     let mut res = Ok(());
 
diff --git a/src/receive_imf.rs b/src/receive_imf.rs
index efce9d9eb..79ee1efdb 100644
--- a/src/receive_imf.rs
+++ b/src/receive_imf.rs
@@ -1,7 +1,7 @@
 //! Internet Message Format reception pipeline.
 
 use std::cmp;
-use std::collections::{BTreeMap, BTreeSet, HashSet};
+use std::collections::{BTreeMap, BTreeSet};
 use std::iter;
 use std::sync::LazyLock;
 
@@ -1927,7 +1927,7 @@ async fn add_parts(
         && chat_id.get_ephemeral_timer(context).await? != ephemeral_timer
     {
         let chat_contacts =
-            HashSet::<ContactId>::from_iter(chat::get_chat_contacts(context, chat_id).await?);
+            BTreeSet::<ContactId>::from_iter(chat::get_chat_contacts(context, chat_id).await?);
         let is_from_in_chat =
             !chat_contacts.contains(&ContactId::SELF) || chat_contacts.contains(&from_id);
 
@@ -2462,7 +2462,7 @@ async fn handle_edit_delete(
         // See `message::delete_msgs_ex()`, unlike edit requests, DC doesn't send unencrypted
         // deletion requests, so there's no need to support them.
         if part.param.get_bool(Param::GuaranteeE2ee).unwrap_or(false) {
-            let mut modified_chat_ids = HashSet::new();
+            let mut modified_chat_ids = BTreeSet::new();
             let mut msg_ids = Vec::new();
 
             let rfc724_mid_vec: Vec<&str> = rfc724_mid_list.split_whitespace().collect();
@@ -3094,7 +3094,7 @@ async fn apply_group_changes(
     let mut better_msg = None;
     let mut silent = false;
     let chat_contacts =
-        HashSet::<ContactId>::from_iter(chat::get_chat_contacts(context, chat.id).await?);
+        BTreeSet::<ContactId>::from_iter(chat::get_chat_contacts(context, chat.id).await?);
     let is_from_in_chat =
         !chat_contacts.contains(&ContactId::SELF) || chat_contacts.contains(&from_id);
 
@@ -3172,8 +3172,8 @@ async fn apply_group_changes(
             && chat.member_list_is_stale(context).await?
         {
             info!(context, "Member list is stale.");
-            let mut new_members: HashSet<ContactId> =
-                HashSet::from_iter(to_ids_flat.iter().copied());
+            let mut new_members: BTreeSet<ContactId> =
+                BTreeSet::from_iter(to_ids_flat.iter().copied());
             new_members.insert(ContactId::SELF);
             if !from_id.is_special() {
                 new_members.insert(from_id);
@@ -3217,7 +3217,7 @@ async fn apply_group_changes(
             )
             .await?;
         } else {
-            let mut new_members: HashSet<ContactId>;
+            let mut new_members: BTreeSet<ContactId>;
             // True if a Delta Chat client has explicitly and really added our primary address to an
             // already existing group.
             let self_added =
@@ -3228,7 +3228,7 @@ async fn apply_group_changes(
                     false
                 };
             if self_added {
-                new_members = HashSet::from_iter(to_ids_flat.iter().copied());
+                new_members = BTreeSet::from_iter(to_ids_flat.iter().copied());
                 new_members.insert(ContactId::SELF);
                 if !from_id.is_special() && from_is_key_contact != chat.grpid.is_empty() {
                     new_members.insert(from_id);
@@ -3279,7 +3279,7 @@ async fn apply_group_changes(
             .await?;
     }
 
-    let new_chat_contacts = HashSet::<ContactId>::from_iter(
+    let new_chat_contacts = BTreeSet::<ContactId>::from_iter(
         chat::get_chat_contacts(context, chat.id)
             .await?
             .iter()
@@ -3287,11 +3287,11 @@ async fn apply_group_changes(
     );
 
     // These are for adding info messages about implicit membership changes.
-    let mut added_ids: HashSet<ContactId> = new_chat_contacts
+    let mut added_ids: BTreeSet<ContactId> = new_chat_contacts
         .difference(&chat_contacts)
         .copied()
         .collect();
-    let mut removed_ids: HashSet<ContactId> = chat_contacts
+    let mut removed_ids: BTreeSet<ContactId> = chat_contacts
         .difference(&new_chat_contacts)
         .copied()
         .collect();
@@ -3513,8 +3513,8 @@ async fn apply_chat_name_avatar_and_description_changes(
 #[expect(clippy::arithmetic_side_effects)]
 async fn group_changes_msgs(
     context: &Context,
-    added_ids: &HashSet<ContactId>,
-    removed_ids: &HashSet<ContactId>,
+    added_ids: &BTreeSet<ContactId>,
+    removed_ids: &BTreeSet<ContactId>,
     chat_id: ChatId,
 ) -> Result<Vec<(String, SystemMessage, Option<ContactId>)>> {
     let mut group_changes_msgs: Vec<(String, SystemMessage, Option<ContactId>)> = Vec::new();
diff --git a/src/sync.rs b/src/sync.rs
index 3e87bb05e..8b050456d 100644
--- a/src/sync.rs
+++ b/src/sync.rs
@@ -19,7 +19,7 @@ use crate::token::Namespace;
 use crate::tools::time;
 use crate::transport::{ConfiguredLoginParamJson, sync_transports};
 use crate::{message, stock_str, token};
-use std::collections::HashSet;
+use std::collections::BTreeSet;
 
 /// Whether to send device sync messages. Aimed for usage in the internal API.
 #[derive(Debug, PartialEq)]
@@ -383,7 +383,7 @@ impl Context {
     }
 
     async fn sync_message_deletion(&self, msgs: &Vec<String>) -> Result<()> {
-        let mut modified_chat_ids = HashSet::new();
+        let mut modified_chat_ids = BTreeSet::new();
         let mut msg_ids = Vec::new();
         for rfc724_mid in msgs {
             if let Some(msg_id) = message::rfc724_mid_exists(self, rfc724_mid).await? {