diff --git a/lib/types/DataSources.ts b/lib/types/DataSources.ts
index 685f914..c499d30 100644
--- a/lib/types/DataSources.ts
+++ b/lib/types/DataSources.ts
@@ -53,14 +53,14 @@ export interface GroupCache<LoadedValue> extends GroupWriteCache<LoadedValue> {
   getExpirationTimeFromGroup: (key: string, group: string) => Promise<number | undefined>
 }
 
-export interface DataSource<LoadedValue, LoadParams = undefined> {
+export interface DataSource<LoadedValue, LoadParams = string> {
   get: (loadParams: LoadParams) => Promise<LoadedValue | undefined | null>
   getMany: (keys: string[], loadParams?: LoadParams) => Promise<LoadedValue[]>
 
   name: string
 }
 
-export interface GroupDataSource<LoadedValue, LoadParams = undefined> {
+export interface GroupDataSource<LoadedValue, LoadParams = string> {
   getFromGroup: (loadParams: LoadParams, group: string) => Promise<LoadedValue | undefined | null>
   getManyFromGroup: (keys: string[], group: string, loadParams?: LoadParams) => Promise<LoadedValue[]>