diff --git a/packages/core/src/internal/bookmark.ts b/packages/core/src/internal/bookmark.ts
index 085718f76..059182576 100644
--- a/packages/core/src/internal/bookmark.ts
+++ b/packages/core/src/internal/bookmark.ts
@@ -79,7 +79,7 @@ const EMPTY_BOOKMARK = new Bookmark(null)
  * @return {string[]} value converted to an array.
  */
 function asStringArray(
-  value?: string | string[] | Array<string> | null
+  value?: string | (string | undefined)[] | Array<string | undefined> | null
 ): string[] {
   if (!value) {
     return []
diff --git a/packages/core/src/session.ts b/packages/core/src/session.ts
index 2597a140c..9e94037dd 100644
--- a/packages/core/src/session.ts
+++ b/packages/core/src/session.ts
@@ -55,7 +55,8 @@ class Session {
   private _writeConnectionHolder: ConnectionHolder
   private _open: boolean
   private _hasTx: boolean
-  private _lastBookmark: Bookmark
+  private _bookmarkIn: Bookmark
+  private _bookmarkOut?: string
   private _transactionExecutor: TransactionExecutor
   private _impersonatedUser?: string
   private _onComplete: (meta: any) => void
@@ -117,7 +118,7 @@ class Session {
     this._open = true
     this._hasTx = false
     this._impersonatedUser = impersonatedUser
-    this._lastBookmark = bookmark || Bookmark.empty()
+    this._bookmarkIn = bookmark || Bookmark.empty()
     this._transactionExecutor = _createTransactionExecutor(config)
     this._onComplete = this._onCompleteCallback.bind(this)
     this._databaseNameResolved = this._database !== ''
@@ -150,7 +151,7 @@ class Session {
     return this._run(validatedQuery, params, connection => {
       this._assertSessionIsOpen()
       return (connection as Connection).protocol().run(validatedQuery, params, {
-        bookmark: this._lastBookmark,
+        bookmark: this._bookmarkIn,
         txConfig: autoCommitTxConfig,
         mode: this._mode,
         database: this._database,
@@ -271,7 +272,7 @@ class Session {
       reactive: this._reactive,
       fetchSize: this._fetchSize
     })
-    tx._begin(this._lastBookmark, txConfig)
+    tx._begin(this._bookmarkIn, txConfig)
     return tx
   }
 
@@ -296,10 +297,10 @@ class Session {
   /**
    * Return the bookmark received following the last completed {@link Transaction}.
    *
-   * @return {string[]} A reference to a previous transaction.
+   * @return {string | undefined} A reference to a previous transaction if present.
    */
-  lastBookmark(): string[] {
-    return this._lastBookmark.values()
+  lastBookmark(): string | undefined {
+    return this._bookmarkOut
   }
 
   /**
@@ -360,7 +361,7 @@ class Session {
   /**
    * Sets the resolved database name in the session context.
    * @private
-   * @param {string|undefined} database The resolved database name
+   * @param {string | undefined} database The resolved database name
    * @returns {void}
    */
   _onDatabaseNameResolved(database?: string): void {
@@ -376,12 +377,13 @@ class Session {
   /**
    * Update value of the last bookmark.
    * @private
-   * @param {Bookmark} newBookmark - The new bookmark.
+   * @param {string | undefined} newBookmark - The new bookmark.
    * @returns {void}
    */
-  _updateBookmark(newBookmark?: Bookmark): void {
-    if (newBookmark && !newBookmark.isEmpty()) {
-      this._lastBookmark = newBookmark
+  _updateBookmark(newBookmark?: string): void {
+    if (newBookmark !== undefined) {
+      this._bookmarkIn = new Bookmark(newBookmark)
+      this._bookmarkOut = newBookmark
     }
   }
 
@@ -414,8 +416,8 @@ class Session {
    * @param {Object} meta Connection metadatada
    * @returns {void}
    */
-  _onCompleteCallback(meta: { bookmark: string | string[] }): void {
-    this._updateBookmark(new Bookmark(meta.bookmark))
+  _onCompleteCallback(meta: { bookmark: string }): void {
+    this._updateBookmark(meta.bookmark)
   }
 
   /**
diff --git a/packages/core/src/transaction.ts b/packages/core/src/transaction.ts
index f48a63a11..5f8f96587 100644
--- a/packages/core/src/transaction.ts
+++ b/packages/core/src/transaction.ts
@@ -46,7 +46,7 @@ class Transaction {
   private _reactive: boolean
   private _state: any
   private _onClose: () => void
-  private _onBookmark: (bookmark: Bookmark) => void
+  private _onBookmark: (bookmark: string | undefined ) => void
   private _onConnection: () => void
   private _onError: (error: Error) => Promise<Connection | void>
   private _onComplete: (metadata: any) => void
@@ -58,7 +58,7 @@ class Transaction {
    * @constructor
    * @param {ConnectionHolder} connectionHolder - the connection holder to get connection from.
    * @param {function()} onClose - Function to be called when transaction is committed or rolled back.
-   * @param {function(bookmark: Bookmark)} onBookmark callback invoked when new bookmark is produced.
+   * @param {function(bookmark: string | undefined)} onBookmark callback invoked when new bookmark is produced.
    * * @param {function()} onConnection - Function to be called when a connection is obtained to ensure the conneciton
    * is not yet released.
    * @param {boolean} reactive whether this transaction generates reactive streams
@@ -76,7 +76,7 @@ class Transaction {
   }: {
     connectionHolder: ConnectionHolder
     onClose: () => void
-    onBookmark: (bookmark: Bookmark) => void
+    onBookmark: (bookmark: string | undefined) => void
     onConnection: () => void
     reactive: boolean
     fetchSize: number
@@ -226,8 +226,8 @@ class Transaction {
    * @param {object} meta The meta with bookmark
    * @returns {void}
    */
-  _onCompleteCallback(meta: { bookmark?: string | string[] }): void {
-    this._onBookmark(new Bookmark(meta.bookmark))
+  _onCompleteCallback(meta: { bookmark?: string }): void {
+    this._onBookmark(meta.bookmark)
   }
 }
 
diff --git a/packages/neo4j-driver/test/types/session.test.ts b/packages/neo4j-driver/test/types/session.test.ts
index c3aaa107a..d593e30a1 100644
--- a/packages/neo4j-driver/test/types/session.test.ts
+++ b/packages/neo4j-driver/test/types/session.test.ts
@@ -55,7 +55,7 @@ const txConfig7: TransactionConfig = {
 }
 
 const tx1: Transaction = session.beginTransaction()
-const bookmark: string[] = session.lastBookmark()
+const bookmark: string | undefined = session.lastBookmark()
 
 const promise1: Promise<number> = session.readTransaction((tx: Transaction) => {
   return 10
@@ -173,4 +173,4 @@ const promise6: Promise<number> = session.writeTransaction(
   txConfig4
 )
 
-const lastBookmark: string[] = session.lastBookmark()
+const lastBookmark: string | undefined = session.lastBookmark()
diff --git a/packages/testkit-backend/src/request-handlers.js b/packages/testkit-backend/src/request-handlers.js
index a27e7526d..4d85e2d72 100644
--- a/packages/testkit-backend/src/request-handlers.js
+++ b/packages/testkit-backend/src/request-handlers.js
@@ -288,7 +288,11 @@ export function TransactionRollback (context, data, wire) {
 export function SessionLastBookmarks (context, data, wire) {
   const { sessionId } = data
   const session = context.getSession(sessionId)
-  const bookmarks = session.lastBookmark()
+  const bookmark = session.lastBookmark()
+  const bookmarks = []
+  if (bookmark !== undefined) {
+    bookmarks.push(bookmark)
+  }
   wire.writeResponse('Bookmarks', { bookmarks })
 }