diff --git a/src/Calc/Valid.php b/src/Calc/Valid.php
index 08851f2..1267559 100644
--- a/src/Calc/Valid.php
+++ b/src/Calc/Valid.php
@@ -92,7 +92,7 @@ class Valid
                     }
 
                     if($option instanceof Checkbox) {
-                        if (isset($this->engine->getVariables()[$option->getId()]) && in_array($opt->getId(), $this->engine->getVariables()[$option->getId()])) {
+                        if (isset($this->engine->getVariables()[$option->getId()]) && is_array($this->engine->getVariables()[$option->getId()]) && in_array($opt->getId(), $this->engine->getVariables()[$option->getId()])) {
                             $opt->setIsSelected(true);
                         } else {
                             $opt->setIsSelected(false);