diff --git a/modules/salesforce_mapping/src/SalesforceMappingFieldPluginBase.php b/modules/salesforce_mapping/src/SalesforceMappingFieldPluginBase.php
index ffa80bc7c171f419e88c9f1884f64b7eb965f459..ba4d600d9b17c4db4871082d4da24e84d1afa76e 100644
--- a/modules/salesforce_mapping/src/SalesforceMappingFieldPluginBase.php
+++ b/modules/salesforce_mapping/src/SalesforceMappingFieldPluginBase.php
@@ -281,7 +281,7 @@ abstract class SalesforceMappingFieldPluginBase extends PluginBase implements Sa
         break;
 
       case 'datetime':
-        if ($drupal_field_type === 'datetime_iso8601') {
+        if ($drupal_field_type === 'datetime_iso8601' && is_string($value)) {
           $value = substr($value, 0, 19);
         }
         break;