diff --git a/core/dbobjectiterator.php b/core/dbobjectiterator.php
index 85e1e5208..8f9311266 100644
--- a/core/dbobjectiterator.php
+++ b/core/dbobjectiterator.php
@@ -38,7 +38,7 @@ interface iDBObjectSetIterator extends Countable
 	 *
 	 * @return int
 	 */
-	public function Count();
+	public function Count(): int;
 
 	/**
 	 * Reset the cursor to the first item in the collection. Equivalent to Seek(0)
@@ -52,7 +52,7 @@ interface iDBObjectSetIterator extends Countable
 	 *
 	 * @param int $iRow
 	 */
-	public function Seek($iPosition);
+	public function Seek($iPosition): void;
 
 	/**
 	 * Fetch the object at the current position in the collection and move the cursor to the next position.
diff --git a/core/dbobjectset.class.php b/core/dbobjectset.class.php
index 57c2da786..fb8ebb43b 100644
--- a/core/dbobjectset.class.php
+++ b/core/dbobjectset.class.php
@@ -842,7 +842,7 @@ class DBObjectSet implements iDBObjectSetIterator
      * @throws \MySQLException
      * @throws \MySQLHasGoneAwayException
      */
-	public function Count()
+	public function Count(): int
 	{
 		if (is_null($this->m_iNumTotalDBRows))
 		{
@@ -1077,14 +1077,13 @@ class DBObjectSet implements iDBObjectSetIterator
      *
      * @param int $iRow
      *
-     * @return int|mixed
-     *
      * @throws \CoreException
      * @throws \MissingQueryArgument
      * @throws \MySQLException
      * @throws \MySQLHasGoneAwayException
+     * @since 3.1.0 N°4517 Now returns void for return type to match parent class and be compatible with PHP 8.1
      */
-	public function Seek($iRow)
+	public function Seek($iRow): void
 	{
 		if (!$this->m_bLoaded) $this->Load();
 
@@ -1093,7 +1092,6 @@ class DBObjectSet implements iDBObjectSetIterator
 		{
 			$this->m_oSQLResult->data_seek($this->m_iCurrRow);
 		}
-		return $this->m_iCurrRow;
 	}
 
     /**
diff --git a/core/ormlinkset.class.inc.php b/core/ormlinkset.class.inc.php
index caa5be16c..f39863755 100644
--- a/core/ormlinkset.class.inc.php
+++ b/core/ormlinkset.class.inc.php
@@ -311,7 +311,7 @@ class ormLinkSet implements iDBObjectSetIterator, Iterator, SeekableIterator
 	 * @throws \CoreUnexpectedValue
 	 * @throws \MySQLException
 	 */
-	public function Count()
+	public function Count(): int
 	{
 		$this->LoadOriginalIds();
 		$iRet = count($this->aPreserved) + count($this->aAdded) + count($this->aModified);
@@ -326,7 +326,7 @@ class ormLinkSet implements iDBObjectSetIterator, Iterator, SeekableIterator
 	 * @throws Exception
 	 * @internal param int $iRow
 	 */
-	public function Seek($iPosition)
+	public function Seek($iPosition): void
 	{
 		$this->LoadOriginalIds();