diff --git a/core/designdocument.class.inc.php b/core/designdocument.class.inc.php
index ae873adba..29c1fe743 100644
--- a/core/designdocument.class.inc.php
+++ b/core/designdocument.class.inc.php
@@ -77,6 +77,7 @@ class DesignDocument extends DOMDocument
 	 *
 	 * @return int
 	 */
+	// Return type union is not supported by PHP 7.4, we can remove the following PHP attribute and add the return type once iTop min PHP version is PHP 8.0+
 	#[\ReturnTypeWillChange]
 	public function save($filename, $options = 0)
 	{
diff --git a/core/oql/oql-parser.php b/core/oql/oql-parser.php
index 0c2c80b74..5bd6d1577 100644
--- a/core/oql/oql-parser.php
+++ b/core/oql/oql-parser.php
@@ -38,7 +38,9 @@ class OQLParser_yyToken implements ArrayAccess
         return isset($this->metadata[$offset]);
     }
 
-    function offsetGet($offset): mixed
+	// Return type mixed is not supported by PHP 7.4, we can remove the following PHP attribute and add the return type once iTop min PHP version is PHP 8.0+
+	#[\ReturnTypeWillChange]
+    function offsetGet($offset)
     {
         return $this->metadata[$offset];
     }
diff --git a/core/ormlinkset.class.inc.php b/core/ormlinkset.class.inc.php
index 937d65ba0..47abb66fe 100644
--- a/core/ormlinkset.class.inc.php
+++ b/core/ormlinkset.class.inc.php
@@ -374,7 +374,9 @@ class ormLinkSet implements iDBObjectSetIterator, Iterator, SeekableIterator
 	 * @throws \MySQLException
 	 * @throws \MySQLHasGoneAwayException
 	 */
-	public function current(): mixed
+	// Return type mixed is not supported by PHP 7.4, we can remove the following PHP attribute and add the return type once iTop min PHP version is PHP 8.0+
+	#[\ReturnTypeWillChange]
+	public function current()
 	{
 		$this->LoadOriginalIds();
 
@@ -439,7 +441,9 @@ class ormLinkSet implements iDBObjectSetIterator, Iterator, SeekableIterator
 	 * @link http://php.net/manual/en/iterator.key.php
 	 * @return mixed scalar on success, or null on failure.
 	 */
-	public function key(): mixed
+	// Return type mixed is not supported by PHP 7.4, we can remove the following PHP attribute and add the return type once iTop min PHP version is PHP 8.0+
+	#[\ReturnTypeWillChange]
+	public function key()
 	{
 		return $this->iCursor;
 	}
diff --git a/core/simplegraph.class.inc.php b/core/simplegraph.class.inc.php
index 1c5304d1a..0e0f5f249 100644
--- a/core/simplegraph.class.inc.php
+++ b/core/simplegraph.class.inc.php
@@ -760,12 +760,16 @@ class RelationTypeIterator implements Iterator
 		$this->iCurrentIdx++;
 	}
 	
-	public function current(): mixed
+	// Return type mixed is not supported by PHP 7.4, we can remove the following PHP attribute and add the return type once iTop min PHP version is PHP 8.0+
+	#[\ReturnTypeWillChange]
+	public function current()
 	{
 		return $this->aList[$this->iCurrentIdx];
 	}
 	
-	public function key(): mixed
+	// Return type mixed is not supported by PHP 7.4, we can remove the following PHP attribute and add the return type once iTop min PHP version is PHP 8.0+
+	#[\ReturnTypeWillChange]
+	public function key()
 	{
 		return $this->iCurrentIdx;
 	}
diff --git a/setup/modelfactory.class.inc.php b/setup/modelfactory.class.inc.php
index 347a2e040..0b03e8028 100644
--- a/setup/modelfactory.class.inc.php
+++ b/setup/modelfactory.class.inc.php
@@ -2538,6 +2538,7 @@ class MFDocument extends \Combodo\iTop\DesignDocument
 	 * @return string
 	 * @throws \Exception
 	 */
+	// Return type union is not supported by PHP 7.4, we can remove the following PHP attribute and add the return type once iTop min PHP version is PHP 8.0+
 	#[\ReturnTypeWillChange]
 	public function saveXML(DOMNode $node = null, $options = 0)
 	{