diff --git a/crates/storage-pg/.sqlx/query-48213d718a256a12540c0aec595ca3e436be423f2d0c868700c6397745ed0455.json b/crates/storage-pg/.sqlx/query-d2a4f5c01603463b78198529d295f7f121769ea5730d01c20c0ddbcdc79a5716.json
similarity index 88%
rename from crates/storage-pg/.sqlx/query-48213d718a256a12540c0aec595ca3e436be423f2d0c868700c6397745ed0455.json
rename to crates/storage-pg/.sqlx/query-d2a4f5c01603463b78198529d295f7f121769ea5730d01c20c0ddbcdc79a5716.json
index 52c7ab0bc..171a83623 100644
--- a/crates/storage-pg/.sqlx/query-48213d718a256a12540c0aec595ca3e436be423f2d0c868700c6397745ed0455.json
+++ b/crates/storage-pg/.sqlx/query-d2a4f5c01603463b78198529d295f7f121769ea5730d01c20c0ddbcdc79a5716.json
@@ -1,6 +1,6 @@
 {
   "db_name": "PostgreSQL",
-  "query": "\n                SELECT user_id\n                     , username\n                     , created_at\n                     , locked_at\n                     , deactivated_at\n                     , can_request_admin\n                FROM users\n                WHERE username = $1\n            ",
+  "query": "\n                SELECT user_id\n                     , username\n                     , created_at\n                     , locked_at\n                     , deactivated_at\n                     , can_request_admin\n                FROM users\n                WHERE LOWER(username) = LOWER($1)\n            ",
   "describe": {
     "columns": [
       {
@@ -48,5 +48,5 @@
       false
     ]
   },
-  "hash": "48213d718a256a12540c0aec595ca3e436be423f2d0c868700c6397745ed0455"
+  "hash": "d2a4f5c01603463b78198529d295f7f121769ea5730d01c20c0ddbcdc79a5716"
 }
diff --git a/crates/storage-pg/migrations/20250410121612_users_lower_username_idx.sql b/crates/storage-pg/migrations/20250410121612_users_lower_username_idx.sql
new file mode 100644
index 000000000..625e07e1b
--- /dev/null
+++ b/crates/storage-pg/migrations/20250410121612_users_lower_username_idx.sql
@@ -0,0 +1,10 @@
+-- no-transaction
+-- Copyright 2025 New Vector Ltd.
+--
+-- SPDX-License-Identifier: AGPL-3.0-only
+-- Please see LICENSE in the repository root for full details.
+
+-- Create an index on the username column, lower-cased, so that we can lookup
+-- usernames in a case-insensitive manner.
+CREATE INDEX CONCURRENTLY users_lower_username_idx
+    ON users (LOWER(username));
diff --git a/crates/storage-pg/src/user/mod.rs b/crates/storage-pg/src/user/mod.rs
index 2f5036134..abcd21ef0 100644
--- a/crates/storage-pg/src/user/mod.rs
+++ b/crates/storage-pg/src/user/mod.rs
@@ -175,7 +175,7 @@ impl UserRepository for PgUserRepository<'_> {
                      , deactivated_at
                      , can_request_admin
                 FROM users
-                WHERE username = $1
+                WHERE LOWER(username) = LOWER($1)
             "#,
             username,
         )
diff --git a/crates/storage/src/user/mod.rs b/crates/storage/src/user/mod.rs
index 01feebbc4..395c6e615 100644
--- a/crates/storage/src/user/mod.rs
+++ b/crates/storage/src/user/mod.rs
@@ -155,7 +155,7 @@ pub trait UserRepository: Send + Sync {
     /// Returns [`Self::Error`] if the underlying repository fails
     async fn lookup(&mut self, id: Ulid) -> Result<Option<User>, Self::Error>;
 
-    /// Find a [`User`] by its username
+    /// Find a [`User`] by its username, in a case-insensitive manner
     ///
     /// Returns `None` if no [`User`] was found
     ///