diff --git a/setup/modelfactory.class.inc.php b/setup/modelfactory.class.inc.php
index acea63e85..3ef265935 100644
--- a/setup/modelfactory.class.inc.php
+++ b/setup/modelfactory.class.inc.php
@@ -1466,7 +1466,7 @@ EOF
 		switch ($sAlteration) {
 			case '':
 				if ($oNodeClone->hasAttribute('id')) {
-					$oNodeClone->setAttribute('_delta', 'must_exist');
+					$oNodeClone->setAttribute('_delta', 'merge');
 				}
 				break;
 			case 'added':
diff --git a/tests/php-unit-tests/unitary-tests/setup/ModelFactoryTest.php b/tests/php-unit-tests/unitary-tests/setup/ModelFactoryTest.php
index b5ff5a8db..aaf514ce9 100644
--- a/tests/php-unit-tests/unitary-tests/setup/ModelFactoryTest.php
+++ b/tests/php-unit-tests/unitary-tests/setup/ModelFactoryTest.php
@@ -678,6 +678,56 @@ XML
 <nodeA>
 	<nodeB>Luke Banner</nodeB>
 </nodeA>
+XML
+		];
+		$aDeltas['_delta="define_and_must_exits"'] = [
+			'sInitialXML' => <<<XML
+<nodeA>
+</nodeA>
+XML
+			,
+			'sDeltaXML' => <<<XML
+<nodeA>
+	<nodeB id="Banner" _delta="define"/>
+	<nodeB id="Banner" _delta="must_exist">
+		<nodeC _delta="define"/>
+	</nodeB>
+</nodeA>
+XML
+			,
+			'sExpectedXML' => <<<XML
+<nodeA>
+  <nodeB id="Banner">
+    <nodeC/>
+  </nodeB>
+</nodeA>
+XML
+		];
+		$aDeltas['_delta="define_and_must_exits_fails"'] = [
+			'sInitialXML' => <<<XML
+<nodeA>
+</nodeA>
+XML
+			,
+			'sDeltaXML' => <<<XML
+<nodeA>
+	<nodeB id="Banner" _delta="define">
+		<nodeE/>
+	</nodeB>
+	<nodeB id="Banner" _delta="must_exist">
+		<nodeC _delta="define_if_not_exists">
+			<nodeD id="Bruce" _delta="define"/>
+		</nodeC>
+	</nodeB>
+</nodeA>
+XML
+			,
+			'sExpectedXML' => <<<XML
+<nodeA>
+  <nodeB id="Banner">
+    <nodeC/>
+  </nodeB>
+</nodeA>
 XML
 		];