diff --git a/roomserver/internal/api.go b/roomserver/internal/api.go
index 6d7c8fcf..efe9bdcd 100644
--- a/roomserver/internal/api.go
+++ b/roomserver/internal/api.go
@@ -20,7 +20,7 @@ type RoomserverInternalAPI struct {
 	ServerName           gomatrixserverlib.ServerName
 	KeyRing              gomatrixserverlib.JSONVerifier
 	FedClient            *gomatrixserverlib.FederationClient
-	OutputRoomEventTopic string     // Kafka topic for new output room events
-	mutex                sync.Mutex // Protects calls to processRoomEvent
+	OutputRoomEventTopic string   // Kafka topic for new output room events
+	mutexes              sync.Map // room ID -> *sync.Mutex, protects calls to processRoomEvent
 	fsAPI                fsAPI.FederationSenderInternalAPI
 }
diff --git a/roomserver/internal/input.go b/roomserver/internal/input.go
index 2af3e62d..e85e9830 100644
--- a/roomserver/internal/input.go
+++ b/roomserver/internal/input.go
@@ -18,6 +18,7 @@ package internal
 import (
 	"context"
 	"encoding/json"
+	"sync"
 
 	"github.com/Shopify/sarama"
 	"github.com/matrix-org/dendrite/roomserver/api"
@@ -71,13 +72,18 @@ func (r *RoomserverInternalAPI) InputRoomEvents(
 	request *api.InputRoomEventsRequest,
 	response *api.InputRoomEventsResponse,
 ) (err error) {
-	// We lock as processRoomEvent can only be called once at a time
-	r.mutex.Lock()
-	defer r.mutex.Unlock()
-	for i := range request.InputRoomEvents {
+	for i, e := range request.InputRoomEvents {
+		roomID := "global"
+		if r.DB.SupportsConcurrentRoomInputs() {
+			roomID = e.Event.RoomID()
+		}
+		mutex, _ := r.mutexes.LoadOrStore(roomID, &sync.Mutex{})
+		mutex.(*sync.Mutex).Lock()
 		if response.EventID, err = r.processRoomEvent(ctx, request.InputRoomEvents[i]); err != nil {
+			mutex.(*sync.Mutex).Unlock()
 			return err
 		}
+		mutex.(*sync.Mutex).Unlock()
 	}
 	return nil
 }
diff --git a/roomserver/storage/interface.go b/roomserver/storage/interface.go
index 988fc908..545885f7 100644
--- a/roomserver/storage/interface.go
+++ b/roomserver/storage/interface.go
@@ -24,6 +24,8 @@ import (
 )
 
 type Database interface {
+	// Do we support processing input events for more than one room at a time?
+	SupportsConcurrentRoomInputs() bool
 	// Store the room state at an event in the database
 	AddState(
 		ctx context.Context,
diff --git a/roomserver/storage/postgres/events_table.go b/roomserver/storage/postgres/events_table.go
index bdbf5e7c..e66efb09 100644
--- a/roomserver/storage/postgres/events_table.go
+++ b/roomserver/storage/postgres/events_table.go
@@ -276,9 +276,10 @@ func (s *eventStatements) BulkSelectStateAtEventByID(
 }
 
 func (s *eventStatements) UpdateEventState(
-	ctx context.Context, eventNID types.EventNID, stateNID types.StateSnapshotNID,
+	ctx context.Context, txn *sql.Tx, eventNID types.EventNID, stateNID types.StateSnapshotNID,
 ) error {
-	_, err := s.updateEventStateStmt.ExecContext(ctx, int64(eventNID), int64(stateNID))
+	stmt := sqlutil.TxStmt(txn, s.updateEventStateStmt)
+	_, err := stmt.ExecContext(ctx, int64(eventNID), int64(stateNID))
 	return err
 }
 
diff --git a/roomserver/storage/postgres/published_table.go b/roomserver/storage/postgres/published_table.go
index 23a9b067..440ae784 100644
--- a/roomserver/storage/postgres/published_table.go
+++ b/roomserver/storage/postgres/published_table.go
@@ -19,6 +19,7 @@ import (
 	"database/sql"
 
 	"github.com/matrix-org/dendrite/internal"
+	"github.com/matrix-org/dendrite/internal/sqlutil"
 	"github.com/matrix-org/dendrite/roomserver/storage/shared"
 	"github.com/matrix-org/dendrite/roomserver/storage/tables"
 )
@@ -63,9 +64,10 @@ func NewPostgresPublishedTable(db *sql.DB) (tables.Published, error) {
 }
 
 func (s *publishedStatements) UpsertRoomPublished(
-	ctx context.Context, roomID string, published bool,
+	ctx context.Context, txn *sql.Tx, roomID string, published bool,
 ) (err error) {
-	_, err = s.upsertPublishedStmt.ExecContext(ctx, roomID, published)
+	stmt := sqlutil.TxStmt(txn, s.upsertPublishedStmt)
+	_, err = stmt.ExecContext(ctx, roomID, published)
 	return
 }
 
diff --git a/roomserver/storage/postgres/room_aliases_table.go b/roomserver/storage/postgres/room_aliases_table.go
index 85042c54..b603a673 100644
--- a/roomserver/storage/postgres/room_aliases_table.go
+++ b/roomserver/storage/postgres/room_aliases_table.go
@@ -20,6 +20,7 @@ import (
 	"database/sql"
 
 	"github.com/matrix-org/dendrite/internal"
+	"github.com/matrix-org/dendrite/internal/sqlutil"
 	"github.com/matrix-org/dendrite/roomserver/storage/shared"
 	"github.com/matrix-org/dendrite/roomserver/storage/tables"
 )
@@ -77,9 +78,10 @@ func NewPostgresRoomAliasesTable(db *sql.DB) (tables.RoomAliases, error) {
 }
 
 func (s *roomAliasesStatements) InsertRoomAlias(
-	ctx context.Context, alias string, roomID string, creatorUserID string,
+	ctx context.Context, txn *sql.Tx, alias string, roomID string, creatorUserID string,
 ) (err error) {
-	_, err = s.insertRoomAliasStmt.ExecContext(ctx, alias, roomID, creatorUserID)
+	stmt := sqlutil.TxStmt(txn, s.insertRoomAliasStmt)
+	_, err = stmt.ExecContext(ctx, alias, roomID, creatorUserID)
 	return
 }
 
@@ -125,8 +127,9 @@ func (s *roomAliasesStatements) SelectCreatorIDFromAlias(
 }
 
 func (s *roomAliasesStatements) DeleteRoomAlias(
-	ctx context.Context, alias string,
+	ctx context.Context, txn *sql.Tx, alias string,
 ) (err error) {
-	_, err = s.deleteRoomAliasStmt.ExecContext(ctx, alias)
+	stmt := sqlutil.TxStmt(txn, s.deleteRoomAliasStmt)
+	_, err = stmt.ExecContext(ctx, alias)
 	return
 }
diff --git a/roomserver/storage/shared/storage.go b/roomserver/storage/shared/storage.go
index 766d4f20..56c2b029 100644
--- a/roomserver/storage/shared/storage.go
+++ b/roomserver/storage/shared/storage.go
@@ -44,6 +44,10 @@ type Database struct {
 	RedactionsTable     tables.Redactions
 }
 
+func (d *Database) SupportsConcurrentRoomInputs() bool {
+	return true
+}
+
 func (d *Database) EventTypeNIDs(
 	ctx context.Context, eventTypes []string,
 ) (map[string]types.EventTypeNID, error) {
@@ -114,8 +118,8 @@ func (d *Database) EventNIDs(
 func (d *Database) SetState(
 	ctx context.Context, eventNID types.EventNID, stateNID types.StateSnapshotNID,
 ) error {
-	return d.Writer.Do(d.DB, nil, func(_ *sql.Tx) error {
-		return d.EventsTable.UpdateEventState(ctx, eventNID, stateNID)
+	return d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		return d.EventsTable.UpdateEventState(ctx, txn, eventNID, stateNID)
 	})
 }
 
@@ -224,8 +228,8 @@ func (d *Database) GetRoomVersionForRoomNID(
 }
 
 func (d *Database) SetRoomAlias(ctx context.Context, alias string, roomID string, creatorUserID string) error {
-	return d.Writer.Do(d.DB, nil, func(_ *sql.Tx) error {
-		return d.RoomAliasesTable.InsertRoomAlias(ctx, alias, roomID, creatorUserID)
+	return d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		return d.RoomAliasesTable.InsertRoomAlias(ctx, txn, alias, roomID, creatorUserID)
 	})
 }
 
@@ -244,8 +248,8 @@ func (d *Database) GetCreatorIDForAlias(
 }
 
 func (d *Database) RemoveRoomAlias(ctx context.Context, alias string) error {
-	return d.Writer.Do(d.DB, nil, func(_ *sql.Tx) error {
-		return d.RoomAliasesTable.DeleteRoomAlias(ctx, alias)
+	return d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		return d.RoomAliasesTable.DeleteRoomAlias(ctx, txn, alias)
 	})
 }
 
@@ -253,8 +257,8 @@ func (d *Database) GetMembership(
 	ctx context.Context, roomNID types.RoomNID, requestSenderUserID string,
 ) (membershipEventNID types.EventNID, stillInRoom bool, err error) {
 	var requestSenderUserNID types.EventStateKeyNID
-	err = d.Writer.Do(d.DB, nil, func(_ *sql.Tx) error {
-		requestSenderUserNID, err = d.assignStateKeyNID(ctx, nil, requestSenderUserID)
+	err = d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		requestSenderUserNID, err = d.assignStateKeyNID(ctx, txn, requestSenderUserID)
 		return err
 	})
 	if err != nil {
@@ -471,8 +475,8 @@ func (d *Database) StoreEvent(
 }
 
 func (d *Database) PublishRoom(ctx context.Context, roomID string, publish bool) error {
-	return d.Writer.Do(d.DB, nil, func(_ *sql.Tx) error {
-		return d.PublishedTable.UpsertRoomPublished(ctx, roomID, publish)
+	return d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		return d.PublishedTable.UpsertRoomPublished(ctx, txn, roomID, publish)
 	})
 }
 
diff --git a/roomserver/storage/sqlite3/events_table.go b/roomserver/storage/sqlite3/events_table.go
index 26ea1d41..a866c85d 100644
--- a/roomserver/storage/sqlite3/events_table.go
+++ b/roomserver/storage/sqlite3/events_table.go
@@ -279,9 +279,10 @@ func (s *eventStatements) BulkSelectStateAtEventByID(
 }
 
 func (s *eventStatements) UpdateEventState(
-	ctx context.Context, eventNID types.EventNID, stateNID types.StateSnapshotNID,
+	ctx context.Context, txn *sql.Tx, eventNID types.EventNID, stateNID types.StateSnapshotNID,
 ) error {
-	_, err := s.updateEventStateStmt.ExecContext(ctx, int64(stateNID), int64(eventNID))
+	stmt := sqlutil.TxStmt(txn, s.updateEventStateStmt)
+	_, err := stmt.ExecContext(ctx, int64(stateNID), int64(eventNID))
 	return err
 }
 
diff --git a/roomserver/storage/sqlite3/published_table.go b/roomserver/storage/sqlite3/published_table.go
index 1d6ccd56..dcf6f697 100644
--- a/roomserver/storage/sqlite3/published_table.go
+++ b/roomserver/storage/sqlite3/published_table.go
@@ -19,6 +19,7 @@ import (
 	"database/sql"
 
 	"github.com/matrix-org/dendrite/internal"
+	"github.com/matrix-org/dendrite/internal/sqlutil"
 	"github.com/matrix-org/dendrite/roomserver/storage/shared"
 	"github.com/matrix-org/dendrite/roomserver/storage/tables"
 )
@@ -65,9 +66,10 @@ func NewSqlitePublishedTable(db *sql.DB) (tables.Published, error) {
 }
 
 func (s *publishedStatements) UpsertRoomPublished(
-	ctx context.Context, roomID string, published bool,
+	ctx context.Context, txn *sql.Tx, roomID string, published bool,
 ) error {
-	_, err := s.upsertPublishedStmt.ExecContext(ctx, roomID, published)
+	stmt := sqlutil.TxStmt(txn, s.upsertPublishedStmt)
+	_, err := stmt.ExecContext(ctx, roomID, published)
 	return err
 }
 
diff --git a/roomserver/storage/sqlite3/room_aliases_table.go b/roomserver/storage/sqlite3/room_aliases_table.go
index a16e97aa..f053e398 100644
--- a/roomserver/storage/sqlite3/room_aliases_table.go
+++ b/roomserver/storage/sqlite3/room_aliases_table.go
@@ -20,6 +20,7 @@ import (
 	"database/sql"
 
 	"github.com/matrix-org/dendrite/internal"
+	"github.com/matrix-org/dendrite/internal/sqlutil"
 	"github.com/matrix-org/dendrite/roomserver/storage/shared"
 	"github.com/matrix-org/dendrite/roomserver/storage/tables"
 )
@@ -81,9 +82,10 @@ func NewSqliteRoomAliasesTable(db *sql.DB) (tables.RoomAliases, error) {
 }
 
 func (s *roomAliasesStatements) InsertRoomAlias(
-	ctx context.Context, alias string, roomID string, creatorUserID string,
+	ctx context.Context, txn *sql.Tx, alias string, roomID string, creatorUserID string,
 ) error {
-	_, err := s.insertRoomAliasStmt.ExecContext(ctx, alias, roomID, creatorUserID)
+	stmt := sqlutil.TxStmt(txn, s.insertRoomAliasStmt)
+	_, err := stmt.ExecContext(ctx, alias, roomID, creatorUserID)
 	return err
 }
 
@@ -131,8 +133,9 @@ func (s *roomAliasesStatements) SelectCreatorIDFromAlias(
 }
 
 func (s *roomAliasesStatements) DeleteRoomAlias(
-	ctx context.Context, alias string,
+	ctx context.Context, txn *sql.Tx, alias string,
 ) error {
-	_, err := s.deleteRoomAliasStmt.ExecContext(ctx, alias)
+	stmt := sqlutil.TxStmt(txn, s.deleteRoomAliasStmt)
+	_, err := stmt.ExecContext(ctx, alias)
 	return err
 }
diff --git a/roomserver/storage/sqlite3/storage.go b/roomserver/storage/sqlite3/storage.go
index 8e3af6b7..874bbbc7 100644
--- a/roomserver/storage/sqlite3/storage.go
+++ b/roomserver/storage/sqlite3/storage.go
@@ -139,6 +139,14 @@ func Open(dbProperties *config.DatabaseOptions) (*Database, error) {
 	return &d, nil
 }
 
+func (d *Database) SupportsConcurrentRoomInputs() bool {
+	// This isn't supported in SQLite mode yet because of issues with
+	// database locks.
+	// TODO: Look at this again - the problem is probably to do with
+	// the membership updaters and latest events updaters.
+	return false
+}
+
 func (d *Database) GetLatestEventsForUpdate(
 	ctx context.Context, roomNID types.RoomNID,
 ) (*shared.LatestEventsUpdater, error) {
diff --git a/roomserver/storage/tables/interface.go b/roomserver/storage/tables/interface.go
index 78273b3c..47c12c2c 100644
--- a/roomserver/storage/tables/interface.go
+++ b/roomserver/storage/tables/interface.go
@@ -42,7 +42,7 @@ type Events interface {
 	// If any of the requested events are missing from the database it returns a types.MissingEventError.
 	// If we do not have the state for any of the requested events it returns a types.MissingEventError.
 	BulkSelectStateAtEventByID(ctx context.Context, eventIDs []string) ([]types.StateAtEvent, error)
-	UpdateEventState(ctx context.Context, eventNID types.EventNID, stateNID types.StateSnapshotNID) error
+	UpdateEventState(ctx context.Context, txn *sql.Tx, eventNID types.EventNID, stateNID types.StateSnapshotNID) error
 	SelectEventSentToOutput(ctx context.Context, txn *sql.Tx, eventNID types.EventNID) (sentToOutput bool, err error)
 	UpdateEventSentToOutput(ctx context.Context, txn *sql.Tx, eventNID types.EventNID) error
 	SelectEventID(ctx context.Context, txn *sql.Tx, eventNID types.EventNID) (eventID string, err error)
@@ -84,11 +84,11 @@ type StateBlock interface {
 }
 
 type RoomAliases interface {
-	InsertRoomAlias(ctx context.Context, alias string, roomID string, creatorUserID string) (err error)
+	InsertRoomAlias(ctx context.Context, txn *sql.Tx, alias string, roomID string, creatorUserID string) (err error)
 	SelectRoomIDFromAlias(ctx context.Context, alias string) (roomID string, err error)
 	SelectAliasesFromRoomID(ctx context.Context, roomID string) ([]string, error)
 	SelectCreatorIDFromAlias(ctx context.Context, alias string) (creatorID string, err error)
-	DeleteRoomAlias(ctx context.Context, alias string) (err error)
+	DeleteRoomAlias(ctx context.Context, txn *sql.Tx, alias string) (err error)
 }
 
 type PreviousEvents interface {
@@ -123,7 +123,7 @@ type Membership interface {
 }
 
 type Published interface {
-	UpsertRoomPublished(ctx context.Context, roomID string, published bool) (err error)
+	UpsertRoomPublished(ctx context.Context, txn *sql.Tx, roomID string, published bool) (err error)
 	SelectPublishedFromRoomID(ctx context.Context, roomID string) (published bool, err error)
 	SelectAllPublishedRooms(ctx context.Context, published bool) ([]string, error)
 }