diff --git a/src/github.com/matrix-org/dendrite/clientapi/auth/storage/accounts/filter_table.go b/src/github.com/matrix-org/dendrite/clientapi/auth/storage/accounts/filter_table.go
index c50cd1fd9..ee57fbf38 100644
--- a/src/github.com/matrix-org/dendrite/clientapi/auth/storage/accounts/filter_table.go
+++ b/src/github.com/matrix-org/dendrite/clientapi/auth/storage/accounts/filter_table.go
@@ -38,12 +38,16 @@ CREATE INDEX IF NOT EXISTS account_filter_localpart ON account_filter(localpart)
 const selectFilterSQL = "" +
 	"SELECT filter FROM account_filter WHERE localpart = $1 AND id = $2"
 
+const selectFilterByContentSQL = "" +
+	"SELECT filter FROM account_filter WHERE localpart = $1 AND filter = $2"
+
 const insertFilterSQL = "" +
 	"INSERT INTO account_filter (filter, id, localpart) VALUES ($1, DEFAULT, $2) RETURNING id"
 
 type filterStatements struct {
-	selectFilterStmt *sql.Stmt
-	insertFilterStmt *sql.Stmt
+	selectFilterStmt          *sql.Stmt
+	selectFilterByContentStmt *sql.Stmt
+	insertFilterStmt          *sql.Stmt
 }
 
 func (s *filterStatements) prepare(db *sql.DB) (err error) {
@@ -54,6 +58,9 @@ func (s *filterStatements) prepare(db *sql.DB) (err error) {
 	if s.selectFilterStmt, err = db.Prepare(selectFilterSQL); err != nil {
 		return
 	}
+	if s.selectFilterByContentStmt, err = db.Prepare(selectFilterByContentSQL); err != nil {
+		return
+	}
 	if s.insertFilterStmt, err = db.Prepare(insertFilterSQL); err != nil {
 		return
 	}
@@ -70,6 +77,15 @@ func (s *filterStatements) selectFilter(
 func (s *filterStatements) insertFilter(
 	ctx context.Context, filter string, localpart string,
 ) (pos string, err error) {
+	var existingFilter string
+
+	// Check if filter already exists in the database
+	err = s.selectFilterByContentStmt.QueryRowContext(ctx,
+		localpart, filter).Scan(&existingFilter)
+	if existingFilter != "" {
+		return existingFilter, err
+	}
+
 	err = s.insertFilterStmt.QueryRowContext(ctx, filter, localpart).Scan(&pos)
 	return
 }