diff --git a/crates/apub/Cargo.toml b/crates/apub/Cargo.toml
index 5b43f1c59..bba2ee90e 100644
--- a/crates/apub/Cargo.toml
+++ b/crates/apub/Cargo.toml
@@ -37,7 +37,7 @@ lemmy_db_views_person_content_combined = { workspace = true, features = [
 lemmy_db_views_search_combined = { workspace = true, features = ["full"] }
 lemmy_utils = { workspace = true, features = ["full"] }
 lemmy_db_schema = { workspace = true, features = ["full"] }
-lemmy_api_utils = { workspace = true }
+lemmy_api_utils = { workspace = true, features = ["full"] }
 lemmy_apub_objects = { workspace = true }
 activitypub_federation = { workspace = true }
 lemmy_db_schema_file = { workspace = true }
diff --git a/crates/apub/src/api/resolve_object.rs b/crates/apub/src/api/resolve_object.rs
index c543c598a..32ef8a959 100644
--- a/crates/apub/src/api/resolve_object.rs
+++ b/crates/apub/src/api/resolve_object.rs
@@ -91,12 +91,14 @@ mod tests {
     let pool = &mut context.pool();
     let data = TestData::create(pool).await?;
 
-    let name = "test_local_user_name";
     let bio = "test_local_user_bio";
 
-    let creator = LocalUserView::create_test_user(pool, name, bio, false).await?;
-    let regular_user = LocalUserView::create_test_user(pool, name, bio, false).await?;
-    let admin_user = LocalUserView::create_test_user(pool, name, bio, true).await?;
+    let creator =
+      LocalUserView::create_test_user(pool, "test_local_user_name_1", bio, false).await?;
+    let regular_user =
+      LocalUserView::create_test_user(pool, "test_local_user_name_2", bio, false).await?;
+    let admin_user =
+      LocalUserView::create_test_user(pool, "test_local_user_name_3", bio, true).await?;
 
     let community = Community::create(
       pool,
diff --git a/migrations/2025-07-10-105316_username-instance-unique/down.sql b/migrations/2025-07-10-105316_username-instance-unique/down.sql
new file mode 100644
index 000000000..01aada259
--- /dev/null
+++ b/migrations/2025-07-10-105316_username-instance-unique/down.sql
@@ -0,0 +1,3 @@
+ALTER TABLE person
+    DROP CONSTRAINT person_name_instance_unique;
+
diff --git a/migrations/2025-07-10-105316_username-instance-unique/up.sql b/migrations/2025-07-10-105316_username-instance-unique/up.sql
new file mode 100644
index 000000000..87aa4e555
--- /dev/null
+++ b/migrations/2025-07-10-105316_username-instance-unique/up.sql
@@ -0,0 +1,12 @@
+-- lemmy requires (username + instance_id) to be unique
+-- delete any existing duplicates
+DELETE FROM person p1 USING person p2
+WHERE p1.id > p2.id
+    AND p1.name = p2.name
+    AND p1.instance_id = p2.instance_id
+    AND NOT (p1.local
+        OR p2.local);
+
+ALTER TABLE person
+    ADD CONSTRAINT person_name_instance_unique UNIQUE (name, instance_id);
+