diff --git a/components/modal/Modal.tsx b/components/modal/Modal.tsx
index fd77f5aa90..51f9143a60 100644
--- a/components/modal/Modal.tsx
+++ b/components/modal/Modal.tsx
@@ -196,7 +196,7 @@ export default class Modal extends React.Component<ModalProps, {}> {
       <Dialog
         {...restProps}
         prefixCls={prefixCls}
-        className={classNames({ [`${prefixCls}-centered`]: centered }, className)}
+        className={classNames({ [`${prefixCls}-centered`]: !!centered }, className)}
         footer={footer === undefined ? defaultFooter : footer}
         visible={visible}
         mousePosition={mousePosition}
diff --git a/components/modal/confirm.tsx b/components/modal/confirm.tsx
index 47dfd6cb2b..b3b50245a9 100644
--- a/components/modal/confirm.tsx
+++ b/components/modal/confirm.tsx
@@ -33,7 +33,7 @@ const ConfirmDialog = (props: ConfirmDialogProps) => {
     prefixCls,
     `${prefixCls}-${props.type}`,
     {
-      [`${prefixCls}-centered`]: props.centered,
+      [`${prefixCls}-centered`]: !!props.centered,
     },
     props.className,
   );