diff --git a/framework/src/Volo.Abp.AspNetCore.Mvc.UI.Bootstrap/TagHelpers/Form/AbpDynamicformTagHelperService.cs b/framework/src/Volo.Abp.AspNetCore.Mvc.UI.Bootstrap/TagHelpers/Form/AbpDynamicformTagHelperService.cs
index acd718757c..733d56b1f2 100644
--- a/framework/src/Volo.Abp.AspNetCore.Mvc.UI.Bootstrap/TagHelpers/Form/AbpDynamicformTagHelperService.cs
+++ b/framework/src/Volo.Abp.AspNetCore.Mvc.UI.Bootstrap/TagHelpers/Form/AbpDynamicformTagHelperService.cs
@@ -127,7 +127,7 @@ public class AbpDynamicFormTagHelperService : AbpTagHelperService<AbpDynamicForm
             return htmlContent;
         }
 
-        var col_class = $"col-12 col-sm-" + TagHelper.ColumnSize;
+        var col_class = $"col-12 col-sm-" + ((int)TagHelper.ColumnSize);
 
         return $"<div class=\"{col_class}\">{htmlContent}</div>";
     }