diff --git a/crates/storage-pg/.sqlx/query-b26ae7dd28f8a756b55a76e80cdedd7be9ba26435ea4a914421483f8ed832537.json b/crates/storage-pg/.sqlx/query-7f4c4634ada4dc2745530dcca8eee92abf78dfbdf1a25e58a2bc9c14be8035f0.json
similarity index 70%
rename from crates/storage-pg/.sqlx/query-b26ae7dd28f8a756b55a76e80cdedd7be9ba26435ea4a914421483f8ed832537.json
rename to crates/storage-pg/.sqlx/query-7f4c4634ada4dc2745530dcca8eee92abf78dfbdf1a25e58a2bc9c14be8035f0.json
index accc70f5..e9af498f 100644
--- a/crates/storage-pg/.sqlx/query-b26ae7dd28f8a756b55a76e80cdedd7be9ba26435ea4a914421483f8ed832537.json
+++ b/crates/storage-pg/.sqlx/query-7f4c4634ada4dc2745530dcca8eee92abf78dfbdf1a25e58a2bc9c14be8035f0.json
@@ -1,6 +1,6 @@
 {
   "db_name": "PostgreSQL",
-  "query": "\n                INSERT INTO users (user_id, username, created_at)\n                VALUES ($1, $2, $3)\n            ",
+  "query": "\n                INSERT INTO users (user_id, username, created_at)\n                VALUES ($1, $2, $3)\n                ON CONFLICT (username) DO NOTHING\n            ",
   "describe": {
     "columns": [],
     "parameters": {
@@ -12,5 +12,5 @@
     },
     "nullable": []
   },
-  "hash": "b26ae7dd28f8a756b55a76e80cdedd7be9ba26435ea4a914421483f8ed832537"
+  "hash": "7f4c4634ada4dc2745530dcca8eee92abf78dfbdf1a25e58a2bc9c14be8035f0"
 }
diff --git a/crates/storage-pg/src/user/mod.rs b/crates/storage-pg/src/user/mod.rs
index f5cf37d8..7dbf666d 100644
--- a/crates/storage-pg/src/user/mod.rs
+++ b/crates/storage-pg/src/user/mod.rs
@@ -161,10 +161,11 @@ impl<'c> UserRepository for PgUserRepository<'c> {
         let id = Ulid::from_datetime_with_source(created_at.into(), rng);
         tracing::Span::current().record("user.id", tracing::field::display(id));
 
-        sqlx::query!(
+        let res = sqlx::query!(
             r#"
                 INSERT INTO users (user_id, username, created_at)
                 VALUES ($1, $2, $3)
+                ON CONFLICT (username) DO NOTHING
             "#,
             Uuid::from(id),
             username,
@@ -174,6 +175,10 @@ impl<'c> UserRepository for PgUserRepository<'c> {
         .execute(&mut *self.conn)
         .await?;
 
+        // If the user already exists, want to return an error but not poison the
+        // transaction
+        DatabaseError::ensure_affected_rows(&res, 1)?;
+
         Ok(User {
             id,
             username,
diff --git a/crates/storage-pg/src/user/tests.rs b/crates/storage-pg/src/user/tests.rs
index 7036ecbd..cf46bfa6 100644
--- a/crates/storage-pg/src/user/tests.rs
+++ b/crates/storage-pg/src/user/tests.rs
@@ -63,12 +63,38 @@ async fn test_user_repo(pool: PgPool) {
     assert!(repo.user().lookup(user.id).await.unwrap().is_some());
 
     // Adding a second time should give a conflict
+    // It should not poison the transaction though
     assert!(repo
         .user()
         .add(&mut rng, &clock, USERNAME.to_owned())
         .await
         .is_err());
 
+    // Try locking a user
+    assert!(user.is_valid());
+    let user = repo.user().lock(&clock, user).await.unwrap();
+    assert!(!user.is_valid());
+
+    // Check that the property is retrieved on lookup
+    let user = repo.user().lookup(user.id).await.unwrap().unwrap();
+    assert!(!user.is_valid());
+
+    // Locking a second time should not fail
+    let user = repo.user().lock(&clock, user).await.unwrap();
+    assert!(!user.is_valid());
+
+    // Try unlocking a user
+    let user = repo.user().unlock(user).await.unwrap();
+    assert!(user.is_valid());
+
+    // Check that the property is retrieved on lookup
+    let user = repo.user().lookup(user.id).await.unwrap().unwrap();
+    assert!(user.is_valid());
+
+    // Unlocking a second time should not fail
+    let user = repo.user().unlock(user).await.unwrap();
+    assert!(user.is_valid());
+
     repo.save().await.unwrap();
 }