diff --git a/mailbox-core/src/main/java/org/briarproject/mailbox/core/db/JdbcDatabase.kt b/mailbox-core/src/main/java/org/briarproject/mailbox/core/db/JdbcDatabase.kt
index b46c2d3409b5dbade799c805863fe47b0ece68ee..b907191fc10b505e5048dab19c4b78f46f2627a0 100644
--- a/mailbox-core/src/main/java/org/briarproject/mailbox/core/db/JdbcDatabase.kt
+++ b/mailbox-core/src/main/java/org/briarproject/mailbox/core/db/JdbcDatabase.kt
@@ -353,7 +353,7 @@ abstract class JdbcDatabase(private val dbTypes: DatabaseTypes, private val cloc
 
     @Throws(DbException::class)
     override fun getSettings(txn: Transaction, namespace: String): Settings {
-        val connection: Connection = txn.unbox() as Connection
+        val connection: Connection = txn.unbox()
         return getSettings(connection, namespace)
     }
 
@@ -384,7 +384,7 @@ abstract class JdbcDatabase(private val dbTypes: DatabaseTypes, private val cloc
 
     @Throws(DbException::class)
     override fun mergeSettings(txn: Transaction, s: Settings, namespace: String) {
-        val connection: Connection = txn.unbox() as Connection
+        val connection: Connection = txn.unbox()
         mergeSettings(connection, s, namespace)
     }
 
@@ -442,7 +442,7 @@ abstract class JdbcDatabase(private val dbTypes: DatabaseTypes, private val cloc
 
     @Throws(DbException::class)
     override fun addContact(txn: Transaction, contact: Contact) {
-        val connection: Connection = txn.unbox() as Connection
+        val connection: Connection = txn.unbox()
         var ps: PreparedStatement? = null
         try {
             val sql = """INSERT INTO contacts (contactId, token, inbox, outbox)
@@ -464,7 +464,7 @@ abstract class JdbcDatabase(private val dbTypes: DatabaseTypes, private val cloc
 
     @Throws(DbException::class)
     override fun getContact(txn: Transaction, id: Int): Contact? {
-        val connection: Connection = txn.unbox() as Connection
+        val connection: Connection = txn.unbox()
         var ps: PreparedStatement? = null
         var rs: ResultSet? = null
         try {
@@ -490,7 +490,7 @@ abstract class JdbcDatabase(private val dbTypes: DatabaseTypes, private val cloc
 
     @Throws(DbException::class)
     override fun removeContact(txn: Transaction, id: Int) {
-        val connection: Connection = txn.unbox() as Connection
+        val connection: Connection = txn.unbox()
         var ps: PreparedStatement? = null
         try {
             val sql = "DELETE FROM contacts WHERE contactId = ?"
@@ -510,7 +510,7 @@ abstract class JdbcDatabase(private val dbTypes: DatabaseTypes, private val cloc
      */
     @Throws(DbException::class)
     private fun commitTransaction(txn: Transaction) {
-        val connection: Connection = txn.unbox() as Connection
+        val connection: Connection = txn.unbox()
         check(!txn.isCommitted)
         txn.setCommitted()
         commitTransaction(connection)
@@ -524,7 +524,7 @@ abstract class JdbcDatabase(private val dbTypes: DatabaseTypes, private val cloc
      */
     private fun endTransaction(txn: Transaction) {
         try {
-            val connection: Connection = txn.unbox() as Connection
+            val connection: Connection = txn.unbox()
             if (!txn.isCommitted) {
                 abortTransaction(connection)
             }
diff --git a/mailbox-core/src/main/java/org/briarproject/mailbox/core/db/Transaction.kt b/mailbox-core/src/main/java/org/briarproject/mailbox/core/db/Transaction.kt
index 81176661a8f34e4d72cc40f9c5860be56ba19748..45c17a37548bffb69b021824c54213bfb69356e1 100644
--- a/mailbox-core/src/main/java/org/briarproject/mailbox/core/db/Transaction.kt
+++ b/mailbox-core/src/main/java/org/briarproject/mailbox/core/db/Transaction.kt
@@ -17,8 +17,7 @@ class Transaction(
         private set
 
     /**
-     * Returns the database transaction. The type of the returned object
-     * depends on the database implementation.
+     * Returns the database connection.
      */
     fun unbox(): Connection {
         return txn
@@ -26,7 +25,7 @@ class Transaction(
 
     /**
      * Marks the transaction as committed. This method should only be called
-     * by the DatabaseComponent. It must not be called more than once.
+     * by the Database. It must not be called more than once.
      */
     fun setCommitted() {
         check(!isCommitted)
diff --git a/mailbox-core/src/test/java/org/briarproject/mailbox/core/db/JdbcDatabaseTest.kt b/mailbox-core/src/test/java/org/briarproject/mailbox/core/db/JdbcDatabaseTest.kt
index b711dcb000d1a6138ed7bf1cd3609a2963131d9c..1fb1141181e6392c6765105dfe09e6110581e7df 100644
--- a/mailbox-core/src/test/java/org/briarproject/mailbox/core/db/JdbcDatabaseTest.kt
+++ b/mailbox-core/src/test/java/org/briarproject/mailbox/core/db/JdbcDatabaseTest.kt
@@ -93,7 +93,7 @@ abstract class JdbcDatabaseTest {
         merged["baz"] = "qux"
 
         var db: Database = open(false)
-        var txn = db.transaction(false) { txn ->
+        db.transaction(false) { txn ->
             // store 'before'
             db.mergeSettings(txn, before, "namespace")
             assertEquals(before, db.getSettings(txn, "namespace"))