diff --git a/core/metamodel.class.php b/core/metamodel.class.php
index 386c3a12e..ab032712b 100644
--- a/core/metamodel.class.php
+++ b/core/metamodel.class.php
@@ -3074,8 +3074,8 @@ abstract class MetaModel
 		$MANDATORY_ATTRIBUTES = array('attributes');
 		$UNIQUENESS_MANDATORY_KEYS_NB = count($MANDATORY_ATTRIBUTES);
 		$bHasDisabledKey = false;
-		$bHasMissingMandatoryKey = false;
-		$iMissingMandatoryKeysNb = 0;
+		$bHasMissingMandatoryKey = true;
+		$iMissingMandatoryKeysNb = $UNIQUENESS_MANDATORY_KEYS_NB;
 		$bHasAllMandatoryKeysMissing = false;
 		$bHasNonDisabledKeys = false;
 
@@ -3086,6 +3086,12 @@ abstract class MetaModel
 				$bHasDisabledKey = true;
 				continue;
 			}
+			$bHasNonDisabledKeys = true;
+
+			if (in_array($sUniquenessRuleKey, $MANDATORY_ATTRIBUTES, true)) {
+				$bHasMissingMandatoryKey = false;
+				$iMissingMandatoryKeysNb--;
+			}
 
 			if (($sUniquenessRuleKey === 'attributes') && (!empty($aExistingClassFields)))
 			{
@@ -3097,21 +3103,6 @@ abstract class MetaModel
 					}
 				}
 			}
-
-			if (!$aUniquenessRuleProperty)
-			{
-				if (!in_array($sUniquenessRuleKey, $MANDATORY_ATTRIBUTES, true))
-				{
-					continue;
-				}
-
-				$bHasMissingMandatoryKey = true;
-				$iMissingMandatoryKeysNb++;
-
-				continue;
-			}
-
-			$bHasNonDisabledKeys = true;
 		}
 
 		if ($iMissingMandatoryKeysNb == $UNIQUENESS_MANDATORY_KEYS_NB)
diff --git a/test/core/UniquenessConstraintTest.php b/test/core/UniquenessConstraintTest.php
new file mode 100644
index 000000000..7e20e1d6e
--- /dev/null
+++ b/test/core/UniquenessConstraintTest.php
@@ -0,0 +1,77 @@
+<?php
+
+
+namespace Combodo\iTop\Test\UnitTest\Core;
+
+use Combodo\iTop\Test\UnitTest\ItopTestCase;
+
+/**
+ * Class UniquenessConstraintTest
+ *
+ * @since 2.6 N°659 uniqueness constraint
+ *
+ * @package Combodo\iTop\Test\UnitTest\Core
+ */
+class UniquenessConstraintTest extends ItopTestCase
+{
+	protected function setUp()
+	{
+		parent::setUp();
+		require_once(APPROOT.'/core/metamodel.class.php');
+		require_once(APPROOT.'/core/coreexception.class.inc.php');
+	}
+
+	/**
+	 * @covers       MetaModel::CheckUniquenessRuleValidity
+	 * @dataProvider testUniquenessRuleValidityCheckProvider
+	 *
+	 * @param bool $bIsRuleShouldBeValid
+	 * @param bool $bIsRuleOverride
+	 * @param array $aRuleProperties
+	 */
+	public function testUniquenessRuleValidityCheck($bIsRuleShouldBeValid, $bIsRuleOverride, $aRuleProperties)
+	{
+		$bRuleValidResult = true;
+		try
+		{
+			\MetaModel::CheckUniquenessRuleValidity($aRuleProperties, $bIsRuleOverride);
+		}
+		catch (\CoreUnexpectedValue $e)
+		{
+			$bRuleValidResult = false;
+		}
+
+		$this->assertEquals($bIsRuleShouldBeValid, $bRuleValidResult, "Validity test returned $bRuleValidResult");
+	}
+
+	public function testUniquenessRuleValidityCheckProvider()
+	{
+		return array(
+			'simplest rule' => array(true, false, array('attributes' => array('name'))),
+			'with all properties' => array(
+				true,
+				false,
+				array(
+					'attributes' => array('name'),
+					'filter' => 'name != \'\'',
+					'disabled' => false,
+					'is_blocking' => true,
+				),
+			),
+			'only disabled key without ancestor' => array(
+				false,
+				false,
+				array(
+					'disabled' => true,
+				),
+			),
+			'only disabled key with ancestor' => array(
+				true,
+				true,
+				array(
+					'disabled' => true,
+				),
+			),
+		);
+	}
+}
\ No newline at end of file