diff --git a/sources/Forms/Block/AbstractFormBlock.php b/sources/Forms/Block/AbstractFormBlock.php
index 37b8f32be..67e926fe8 100644
--- a/sources/Forms/Block/AbstractFormBlock.php
+++ b/sources/Forms/Block/AbstractFormBlock.php
@@ -183,9 +183,25 @@ abstract class AbstractFormBlock implements IFormBlock
 	 * @param string $sType the type of the input
 	 *
 	 * @return AbstractFormBlock
+	 * @throws \Combodo\iTop\Forms\Block\FormBlockException
 	 */
 	public function AddInput(string $sName, string $sType): AbstractFormBlock
 	{
+		// Check name validity
+		if (preg_match('/(?<name>\w+)/', $sName, $aMatches)) {
+			$sParsedName = $aMatches['name'];
+			if ($sParsedName !== $sName) {
+				$sName = json_encode($sName);
+				$sParsedName = json_encode($sParsedName);
+				$sBlockName = json_encode($this->getName());
+				Throw new FormBlockException("Input $sName does not match $sParsedName for block $sBlockName.");
+			}
+		} else {
+			$sName = json_encode($sName);
+			$sBlockName = json_encode($this->getName());
+			Throw new FormBlockException("Input $sName is not valid for block $sBlockName.");
+		}
+		// Name is valid
 		$this->oIORegister->AddInput($sName, $sType);
 		return $this;
 	}
diff --git a/sources/Forms/Block/Expression/ExpressionFormBlock.php b/sources/Forms/Block/Expression/ExpressionFormBlock.php
index 6a23c2804..4bc276fb7 100644
--- a/sources/Forms/Block/Expression/ExpressionFormBlock.php
+++ b/sources/Forms/Block/Expression/ExpressionFormBlock.php
@@ -13,13 +13,14 @@ use Combodo\iTop\Forms\Register\IORegister;
 use Combodo\iTop\Forms\FormsException;
 use IssueLog;
 use Symfony\Component\Form\FormEvents;
+use Throwable;
 
 /**
  *
  */
 class ExpressionFormBlock extends AbstractFormBlock
 {
-	public const EXPRESSION_PATTERN = "/\[\[(?<input>[^\]]+)]]/";
+	public const EXPRESSION_PATTERN = "/:(?<input>\w+)/";
 
 	// Outputs
 	const OUTPUT_RESULT = "result";
@@ -60,15 +61,22 @@ class ExpressionFormBlock extends AbstractFormBlock
 					if(!$oInput->HasEventValue($sEventType)){
 						throw new FormsException('Unable to compute expression: input '.$aMatches['input'].' has no value for event '.$sEventType.'.');
 					}
-					return $oInput->GetValue($sEventType);
+					$value = $oInput->GetValue($sEventType);
+					if (is_string($value)) {
+						$value = "'$value'";
+					}
+					return $value;
 				},
 				$sExpression);
 
 			$result  = '';
-			eval('$result = '.$sValue.';');
-
-			$this->GetOutput(self::OUTPUT_RESULT)->SetValue($sEventType, new BooleanIOFormat($result));
-			$this->GetOutput(self::OUTPUT_RESULT_INVERT)->SetValue($sEventType, new BooleanIOFormat(!$result));
+			try {
+				eval('$result = '.$sValue.';');
+			} catch (Throwable $e) {
+				IssueLog::Exception(__METHOD__.' expression '.json_encode($sValue).' failed with exception: '.$e->getMessage(), $e);
+			}
+			$this->GetOutput(self::OUTPUT_RESULT)->SetValue($sEventType, new BooleanIOFormat(boolval($result)));
+			$this->GetOutput(self::OUTPUT_RESULT_INVERT)->SetValue($sEventType, new BooleanIOFormat(!boolval($result)));
 			$this->GetOutput(self::OUTPUT_VALUE)->SetValue($sEventType, new RawFormat($result));
 		}
 		catch(\Exception $e){