diff --git a/crates/syn2mas/.sqlx/query-24f6ce6280dc6675ab1ebdde0c5e3db8ff7a686180d71052911879f186ed1c8e.json b/crates/syn2mas/.sqlx/query-24f6ce6280dc6675ab1ebdde0c5e3db8ff7a686180d71052911879f186ed1c8e.json
new file mode 100644
index 000000000..d736336f2
--- /dev/null
+++ b/crates/syn2mas/.sqlx/query-24f6ce6280dc6675ab1ebdde0c5e3db8ff7a686180d71052911879f186ed1c8e.json
@@ -0,0 +1,18 @@
+{
+  "db_name": "PostgreSQL",
+  "query": "\n            INSERT INTO syn2mas__user_passwords\n            (user_password_id, user_id, hashed_password, created_at, version)\n            SELECT * FROM UNNEST($1::UUID[], $2::UUID[], $3::TEXT[], $4::TIMESTAMP WITH TIME ZONE[], $5::INTEGER[])\n            ",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Left": [
+        "UuidArray",
+        "UuidArray",
+        "TextArray",
+        "TimestamptzArray",
+        "Int4Array"
+      ]
+    },
+    "nullable": []
+  },
+  "hash": "24f6ce6280dc6675ab1ebdde0c5e3db8ff7a686180d71052911879f186ed1c8e"
+}
diff --git a/crates/syn2mas/.sqlx/query-c6c7db1d578efc45b9e8c8bfea47cafe3f85d639452fd0593b2773997dfc7425.json b/crates/syn2mas/.sqlx/query-c6c7db1d578efc45b9e8c8bfea47cafe3f85d639452fd0593b2773997dfc7425.json
deleted file mode 100644
index efa2c4d24..000000000
--- a/crates/syn2mas/.sqlx/query-c6c7db1d578efc45b9e8c8bfea47cafe3f85d639452fd0593b2773997dfc7425.json
+++ /dev/null
@@ -1,18 +0,0 @@
-{
-  "db_name": "PostgreSQL",
-  "query": "\n                INSERT INTO syn2mas__user_passwords\n                (user_password_id, user_id, hashed_password, created_at, version)\n                SELECT * FROM UNNEST($1::UUID[], $2::UUID[], $3::TEXT[], $4::TIMESTAMP WITH TIME ZONE[], $5::INTEGER[])\n                ",
-  "describe": {
-    "columns": [],
-    "parameters": {
-      "Left": [
-        "UuidArray",
-        "UuidArray",
-        "TextArray",
-        "TimestamptzArray",
-        "Int4Array"
-      ]
-    },
-    "nullable": []
-  },
-  "hash": "c6c7db1d578efc45b9e8c8bfea47cafe3f85d639452fd0593b2773997dfc7425"
-}
diff --git a/crates/syn2mas/src/mas_writer/mod.rs b/crates/syn2mas/src/mas_writer/mod.rs
index cd64650ac..866b615e9 100644
--- a/crates/syn2mas/src/mas_writer/mod.rs
+++ b/crates/syn2mas/src/mas_writer/mod.rs
@@ -341,6 +341,44 @@ pub struct MasNewUserPassword {
     pub created_at: DateTime<Utc>,
 }
 
+impl WriteBatch for MasNewUserPassword {
+    async fn write_batch(conn: &mut PgConnection, batch: Vec<Self>) -> Result<(), Error> {
+        let mut user_password_ids: Vec<Uuid> = Vec::with_capacity(batch.len());
+        let mut user_ids: Vec<Uuid> = Vec::with_capacity(batch.len());
+        let mut hashed_passwords: Vec<String> = Vec::with_capacity(batch.len());
+        let mut created_ats: Vec<DateTime<Utc>> = Vec::with_capacity(batch.len());
+        let mut versions: Vec<i32> = Vec::with_capacity(batch.len());
+        for MasNewUserPassword {
+            user_password_id,
+            user_id,
+            hashed_password,
+            created_at,
+        } in batch
+        {
+            user_password_ids.push(user_password_id);
+            user_ids.push(user_id.get());
+            hashed_passwords.push(hashed_password);
+            created_ats.push(created_at);
+            versions.push(MIGRATED_PASSWORD_VERSION.into());
+        }
+
+        sqlx::query!(
+            r#"
+            INSERT INTO syn2mas__user_passwords
+            (user_password_id, user_id, hashed_password, created_at, version)
+            SELECT * FROM UNNEST($1::UUID[], $2::UUID[], $3::TEXT[], $4::TIMESTAMP WITH TIME ZONE[], $5::INTEGER[])
+            "#,
+            &user_password_ids[..],
+            &user_ids[..],
+            &hashed_passwords[..],
+            &created_ats[..],
+            &versions[..],
+        ).execute(&mut *conn).await.into_database("writing users to MAS")?;
+
+        Ok(())
+    }
+}
+
 pub struct MasNewEmailThreepid {
     pub user_email_id: Uuid,
     pub user_id: NonNilUuid,
@@ -727,41 +765,15 @@ impl MasWriter {
         &mut self,
         passwords: Vec<MasNewUserPassword>,
     ) -> BoxFuture<'_, Result<(), Error>> {
-        self.writer_pool.spawn_with_connection(move |conn| Box::pin(async move {
-            let mut user_password_ids: Vec<Uuid> = Vec::with_capacity(passwords.len());
-            let mut user_ids: Vec<Uuid> = Vec::with_capacity(passwords.len());
-            let mut hashed_passwords: Vec<String> = Vec::with_capacity(passwords.len());
-            let mut created_ats: Vec<DateTime<Utc>> = Vec::with_capacity(passwords.len());
-            let mut versions: Vec<i32> = Vec::with_capacity(passwords.len());
-            for MasNewUserPassword {
-                user_password_id,
-                user_id,
-                hashed_password,
-                created_at,
-            } in passwords
-            {
-                user_password_ids.push(user_password_id);
-                user_ids.push(user_id.get());
-                hashed_passwords.push(hashed_password);
-                created_ats.push(created_at);
-                versions.push(MIGRATED_PASSWORD_VERSION.into());
-            }
+        self.writer_pool
+            .spawn_with_connection(move |conn| {
+                Box::pin(async move {
+                    MasNewUserPassword::write_batch(conn, passwords).await?;
 
-            sqlx::query!(
-                r#"
-                INSERT INTO syn2mas__user_passwords
-                (user_password_id, user_id, hashed_password, created_at, version)
-                SELECT * FROM UNNEST($1::UUID[], $2::UUID[], $3::TEXT[], $4::TIMESTAMP WITH TIME ZONE[], $5::INTEGER[])
-                "#,
-                &user_password_ids[..],
-                &user_ids[..],
-                &hashed_passwords[..],
-                &created_ats[..],
-                &versions[..],
-            ).execute(&mut *conn).await.into_database("writing users to MAS")?;
-
-            Ok(())
-        })).boxed()
+                    Ok(())
+                })
+            })
+            .boxed()
     }
 
     #[tracing::instrument(skip_all, level = Level::DEBUG)]