diff --git a/userapi/storage/accounts/sqlite3/storage.go b/userapi/storage/accounts/sqlite3/storage.go
index 72b27c8b..2d09090f 100644
--- a/userapi/storage/accounts/sqlite3/storage.go
+++ b/userapi/storage/accounts/sqlite3/storage.go
@@ -40,7 +40,10 @@ type Database struct {
 	threepids    threepidStatements
 	serverName   gomatrixserverlib.ServerName
 
-	createAccountMu sync.Mutex
+	accountsMu     sync.Mutex
+	profilesMu     sync.Mutex
+	accountDatasMu sync.Mutex
+	threepidsMu    sync.Mutex
 }
 
 // NewDatabase creates a new accounts and profiles database
@@ -74,7 +77,15 @@ func NewDatabase(dataSourceName string, serverName gomatrixserverlib.ServerName)
 	if err = t.prepare(db); err != nil {
 		return nil, err
 	}
-	return &Database{db, partitions, a, p, ac, t, serverName, sync.Mutex{}}, nil
+	return &Database{
+		db:                        db,
+		PartitionOffsetStatements: partitions,
+		accounts:                  a,
+		profiles:                  p,
+		accountDatas:              ac,
+		threepids:                 t,
+		serverName:                serverName,
+	}, nil
 }
 
 // GetAccountByPassword returns the account associated with the given localpart and password.
@@ -105,6 +116,8 @@ func (d *Database) GetProfileByLocalpart(
 func (d *Database) SetAvatarURL(
 	ctx context.Context, localpart string, avatarURL string,
 ) error {
+	d.profilesMu.Lock()
+	defer d.profilesMu.Unlock()
 	return d.profiles.setAvatarURL(ctx, localpart, avatarURL)
 }
 
@@ -113,6 +126,8 @@ func (d *Database) SetAvatarURL(
 func (d *Database) SetDisplayName(
 	ctx context.Context, localpart string, displayName string,
 ) error {
+	d.profilesMu.Lock()
+	defer d.profilesMu.Unlock()
 	return d.profiles.setDisplayName(ctx, localpart, displayName)
 }
 
@@ -124,8 +139,12 @@ func (d *Database) CreateGuestAccount(ctx context.Context) (acc *api.Account, er
 	// when the first txn upgrades to a write txn. We also need to lock the account creation else we can
 	// race with CreateAccount
 	// We know we'll be the only process since this is sqlite ;) so a lock here will be all that is needed.
-	d.createAccountMu.Lock()
-	defer d.createAccountMu.Unlock()
+	d.profilesMu.Lock()
+	d.accountDatasMu.Lock()
+	d.accountsMu.Lock()
+	defer d.profilesMu.Unlock()
+	defer d.accountDatasMu.Unlock()
+	defer d.accountsMu.Unlock()
 	err = sqlutil.WithTransaction(d.db, func(txn *sql.Tx) error {
 		var numLocalpart int64
 		numLocalpart, err = d.accounts.selectNewNumericLocalpart(ctx, txn)
@@ -146,8 +165,12 @@ func (d *Database) CreateAccount(
 	ctx context.Context, localpart, plaintextPassword, appserviceID string,
 ) (acc *api.Account, err error) {
 	// Create one account at a time else we can get 'database is locked'.
-	d.createAccountMu.Lock()
-	defer d.createAccountMu.Unlock()
+	d.profilesMu.Lock()
+	d.accountDatasMu.Lock()
+	d.accountsMu.Lock()
+	defer d.profilesMu.Unlock()
+	defer d.accountDatasMu.Unlock()
+	defer d.accountsMu.Unlock()
 	err = sqlutil.WithTransaction(d.db, func(txn *sql.Tx) error {
 		acc, err = d.createAccount(ctx, txn, localpart, plaintextPassword, appserviceID)
 		return err
@@ -155,6 +178,8 @@ func (d *Database) CreateAccount(
 	return
 }
 
+// WARNING! This function assumes that the relevant mutexes have already
+// been taken out by the caller (e.g. CreateAccount or CreateGuestAccount).
 func (d *Database) createAccount(
 	ctx context.Context, txn *sql.Tx, localpart, plaintextPassword, appserviceID string,
 ) (*api.Account, error) {
@@ -196,6 +221,8 @@ func (d *Database) createAccount(
 func (d *Database) SaveAccountData(
 	ctx context.Context, localpart, roomID, dataType string, content json.RawMessage,
 ) error {
+	d.accountDatasMu.Lock()
+	defer d.accountDatasMu.Unlock()
 	return sqlutil.WithTransaction(d.db, func(txn *sql.Tx) error {
 		return d.accountDatas.insertAccountData(ctx, txn, localpart, roomID, dataType, content)
 	})
@@ -247,6 +274,8 @@ var Err3PIDInUse = errors.New("This third-party identifier is already in use")
 func (d *Database) SaveThreePIDAssociation(
 	ctx context.Context, threepid, localpart, medium string,
 ) (err error) {
+	d.threepidsMu.Lock()
+	defer d.threepidsMu.Unlock()
 	return sqlutil.WithTransaction(d.db, func(txn *sql.Tx) error {
 		user, err := d.threepids.selectLocalpartForThreePID(
 			ctx, txn, threepid, medium,
@@ -270,6 +299,8 @@ func (d *Database) SaveThreePIDAssociation(
 func (d *Database) RemoveThreePIDAssociation(
 	ctx context.Context, threepid string, medium string,
 ) (err error) {
+	d.threepidsMu.Lock()
+	defer d.threepidsMu.Unlock()
 	return d.threepids.deleteThreePID(ctx, threepid, medium)
 }