diff --git a/src/_internal/types.ts b/src/_internal/types.ts
index 528dae932..e88039f5f 100644
--- a/src/_internal/types.ts
+++ b/src/_internal/types.ts
@@ -440,9 +440,12 @@ export interface ScopedMutator {
  * @typeParam MutationData - The type of the data returned by the mutator
  */
 export type KeyedMutator<Data> = <MutationData = Data>(
-  data?: Data | Promise<Data | undefined> | MutatorCallback<Data>,
+  data?:
+    | MutationData
+    | Promise<MutationData | undefined>
+    | MutatorCallback<MutationData>,
   opts?: boolean | MutatorOptions<Data, MutationData>
-) => Promise<Data | MutationData | undefined>
+) => Promise<MutationData | undefined>
 
 export type SWRConfiguration<
   Data = any,
diff --git a/src/infinite/index.ts b/src/infinite/index.ts
index f410b5bef..6e51f8574 100644
--- a/src/infinite/index.ts
+++ b/src/infinite/index.ts
@@ -240,13 +240,12 @@ export const infinite = (<Data, Error>(useSWRNext: SWRHook) =>
 
     const mutate = useCallback(
       // eslint-disable-next-line func-names
-      function <T = Data[]>(
+      function <MutationData = Data[]>(
         data?:
-          | undefined
-          | Data[]
-          | Promise<Data[] | undefined>
-          | MutatorCallback<Data[]>,
-        opts?: undefined | boolean | SWRInfiniteMutatorOptions<Data[], T>
+          | MutationData
+          | Promise<MutationData | undefined>
+          | MutatorCallback<MutationData>,
+        opts?: boolean | SWRInfiniteMutatorOptions<Data[], MutationData>
       ) {
         // When passing as a boolean, it's explicitly used to disable/enable
         // revalidation.