diff --git a/sources/Form/Field/MultipleChoicesField.php b/sources/Form/Field/MultipleChoicesField.php
index 0e06a314a..20ab99749 100644
--- a/sources/Form/Field/MultipleChoicesField.php
+++ b/sources/Form/Field/MultipleChoicesField.php
@@ -20,6 +20,7 @@
 namespace Combodo\iTop\Form\Field;
 
 use Closure;
+use utils;
 
 /**
  * Description of MultipleChoicesField
@@ -213,17 +214,25 @@ abstract class MultipleChoicesField extends Field
 	/**
 	 * @inheritDoc
 	 */
-	public function Validate()
-	{
+	public function Validate() {
 		$this->SetValid(true);
 		$this->EmptyErrorMessages();
 
-		foreach ($this->GetValidators() as $oValidator)
-		{
-			foreach ($this->currentValue as $value)
-			{
-				if (!preg_match($oValidator->GetRegExp(true), $value))
-				{
+		if (count($this->currentValue) > 0) {
+			foreach ($this->currentValue as $sCode => $value) {
+				if (utils::IsNullOrEmptyString($value)) {
+					continue;
+				}
+				if (false === array_key_exists($value, $this->aChoices)) {
+					$this->SetValid(false);
+					$this->AddErrorMessage("Value ({$value}) is not part of the field possible values list");
+				}
+			}
+		}
+
+		foreach ($this->GetValidators() as $oValidator) {
+			foreach ($this->currentValue as $value) {
+				if (!preg_match($oValidator->GetRegExp(true), $value)) {
 					$this->SetValid(false);
 					$this->AddErrorMessage($oValidator->GetErrorMessage());
 				}
diff --git a/sources/Form/Field/SelectObjectField.php b/sources/Form/Field/SelectObjectField.php
index a0ae5207c..df547f977 100644
--- a/sources/Form/Field/SelectObjectField.php
+++ b/sources/Form/Field/SelectObjectField.php
@@ -28,6 +28,7 @@ use DBSearch;
 use FieldExpression;
 use MetaModel;
 use ScalarExpression;
+use utils;
 
 /**
  * Description of SelectObjectField
@@ -237,19 +238,40 @@ class SelectObjectField extends Field
 	/**
 	 * @return int
 	 */
-	public function GetControlType()
-	{
+	public function GetControlType() {
 		return $this->iControlType;
 	}
 
 	/**
 	 * @return string|null
 	 */
-	public function GetSearchEndpoint()
-	{
+	public function GetSearchEndpoint() {
 		return $this->sSearchEndpoint;
 	}
 
+	public function Validate() {
+		$sCurrentValueForExtKey = $this->currentValue;
+		if (utils::IsNotNullOrEmptyString($sCurrentValueForExtKey) && ($sCurrentValueForExtKey !== 0)) {
+			$oSearchForExistingCurrentValue = $this->oSearch->DeepClone();
+			$oSearchForExistingCurrentValue->AddCondition('id', $sCurrentValueForExtKey, '=');
+			$oCheckIdAgainstCurrentValueExpression = new BinaryExpression(
+				new FieldExpression('id', $oSearchForExistingCurrentValue->GetClassAlias()), '=', new ScalarExpression($sCurrentValueForExtKey)
+			);
+			$oSearchForExistingCurrentValue->AddConditionExpression($oCheckIdAgainstCurrentValueExpression);
+			$oSetForExistingCurrentValue = new DBObjectSet($oSearchForExistingCurrentValue);
+			$iObjectsCount = $oSetForExistingCurrentValue->CountWithLimit(1);
+
+			if ($iObjectsCount === 0) {
+				$this->SetValid(false);
+				$this->AddErrorMessage("Value $sCurrentValueForExtKey does not match the corresponding filter set");
+
+				return $this->GetValid();
+			}
+		}
+
+		return parent::Validate();
+	}
+
 	/**
 	 * Resets current value if not among allowed ones.
 	 * By default, reset is done ONLY when the field is not read-only.