diff --git a/src/receive_imf.rs b/src/receive_imf.rs
index dc1e19f71..390f6e327 100644
--- a/src/receive_imf.rs
+++ b/src/receive_imf.rs
@@ -1,6 +1,6 @@
 //! Internet Message Format reception pipeline.
 
-use std::collections::{BTreeMap, HashSet};
+use std::collections::{BTreeMap, BTreeSet, HashSet};
 use std::iter;
 use std::sync::LazyLock;
 
@@ -2471,11 +2471,8 @@ async fn lookup_or_create_adhoc_group(
                 .unwrap_or_else(|| "👥📧".to_string())
         });
     let to_ids: Vec<ContactId> = to_ids.iter().filter_map(|x| *x).collect();
-    let mut contact_ids = Vec::with_capacity(to_ids.len() + 1);
-    contact_ids.extend(&to_ids);
-    if !contact_ids.contains(&from_id) {
-        contact_ids.push(from_id);
-    }
+    let mut contact_ids = BTreeSet::<ContactId>::from_iter(to_ids.iter().copied());
+    contact_ids.insert(from_id);
     let trans_fn = |t: &mut rusqlite::Transaction| {
         t.pragma_update(None, "query_only", "0")?;
         t.execute(
diff --git a/src/receive_imf/receive_imf_tests.rs b/src/receive_imf/receive_imf_tests.rs
index 5af832714..c7317a30a 100644
--- a/src/receive_imf/receive_imf_tests.rs
+++ b/src/receive_imf/receive_imf_tests.rs
@@ -1970,18 +1970,23 @@ Message content",
 async fn test_unencrypted_doesnt_goto_self_chat() -> Result<()> {
     let mut tcm = TestContextManager::new();
     let t = &tcm.alice().await;
+    let mut chat_id = None;
 
-    for to in [
+    for (i, to) in [
+        "<alice@example.org>",
         "<alice@example.org>",
         "alice@example.org, alice@example.org",
         "hidden-recipients:;",
-    ] {
+    ]
+    .iter()
+    .enumerate()
+    {
         receive_imf(
             t,
             format!(
                 "Subject: s
 Chat-Version: 1.0
-Message-ID: <foobar@localhost>
+Message-ID: <foobar{i}@localhost>
 To: {to}
 From: <alice@example.org>
 
@@ -1996,9 +2001,14 @@ Your server is hacked. Have a nice day!"
         assert_ne!(msg.chat_id, t.get_self_chat().await.id);
         assert_eq!(msg.from_id, ContactId::SELF);
         assert_eq!(msg.to_id, ContactId::SELF);
-        let chat = Chat::load_from_db(t, msg.chat_id).await?;
-        assert_eq!(chat.typ, Chattype::Group);
-        assert!(!chat.is_encrypted(t).await?);
+        if let Some(chat_id) = chat_id {
+            assert_eq!(msg.chat_id, chat_id);
+        } else {
+            chat_id = Some(msg.chat_id);
+            let chat = Chat::load_from_db(t, msg.chat_id).await?;
+            assert_eq!(chat.typ, Chattype::Group);
+            assert!(!chat.is_encrypted(t).await?);
+        }
     }
     Ok(())
 }