diff --git a/src/Plugin/Block/ModalBlock.php b/src/Plugin/Block/ModalBlock.php
index 55e62d7..907af61 100755
--- a/src/Plugin/Block/ModalBlock.php
+++ b/src/Plugin/Block/ModalBlock.php
@@ -59,6 +59,20 @@ class ModalBlock extends BlockBase implements BlockPluginInterface {
   /**
    * {@inheritdoc}
    */
+  public function blockValidate($form, FormStateInterface $form_state) {
+    if (!empty($form_state->getValue('frequency'))) {
+      if (!is_numeric($form_state->getValue('frequency'))) {
+        $form_state->setErrorByName('frequency', $this->t('This field must be numeric'));
+      }
+    }
+    else {
+      $form_state->setErrorByName('frequency', $this->t('Please fill this field'));
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
   public function blockSubmit($form, FormStateInterface $form_state) {
   	$this->setConfigurationValue('block', $form_state->getValue('block'));
     $this->setConfigurationValue('frequency', $form_state->getValue('frequency'));