diff --git a/src/Plugin/WebformElement/OptionsBase.php b/src/Plugin/WebformElement/OptionsBase.php
index bf72f98b8..bcbd16075 100644
--- a/src/Plugin/WebformElement/OptionsBase.php
+++ b/src/Plugin/WebformElement/OptionsBase.php
@@ -236,6 +236,13 @@ abstract class OptionsBase extends WebformElementBase {
       unset($element['#default_value']);
     }
 
+    // If the #default_value of a radios element is not a value of #options,
+    // we need to unset the #default_value to prevent the below error.
+    // 'An illegal choice has been detected'.
+    if ($element["#type"] == 'radios' && isset($element['#default_value']) && !array_key_exists($element["#default_value"], $element["#options"])) {
+      unset($element['#default_value']);
+    }
+
     // Process custom options properties.
     if ($this->hasProperty('options__properties')) {
       $this->setElementDefaultCallback($element, 'process');