diff --git a/packages/ui/src/composables/useSize.ts b/packages/ui/src/composables/useSize.ts
index 710f7ad82d5..be8ae845fb3 100644
--- a/packages/ui/src/composables/useSize.ts
+++ b/packages/ui/src/composables/useSize.ts
@@ -64,12 +64,12 @@ export const useSizeProps = {
 
   sizesConfig: {
     type: Object as PropType<Record<string, any>>,
-    default: () => sizesConfig[getCurrentInstance()?.type.name ?? 'default'],
+    default: () => sizesConfig[getCurrentInstance()?.type.name ?? 'default'] ?? sizesConfig.default,
   },
 
   fontSizesConfig: {
     type: Object as PropType<Record<string, any>>,
-    default: () => fontSizesConfig[getCurrentInstance()?.type.name ?? 'default'],
+    default: () => fontSizesConfig[getCurrentInstance()?.type.name ?? 'default'] ?? fontSizesConfig.default,
   },
 }