diff --git a/src/core/types.ts b/src/core/types.ts
index ba3fafd529..8d1b94c9ad 100644
--- a/src/core/types.ts
+++ b/src/core/types.ts
@@ -481,7 +481,7 @@ export interface MutationOptions<
   variables?: TVariables
   onMutate?: (
     variables: TVariables
-  ) => Promise<TContext> | Promise<undefined> | TContext | undefined
+  ) => Promise<TContext | undefined> | TContext | undefined
   onSuccess?: (
     data: TData,
     variables: TVariables,
diff --git a/src/react/types.ts b/src/react/types.ts
index 6e6da2f088..ef98597c46 100644
--- a/src/react/types.ts
+++ b/src/react/types.ts
@@ -77,7 +77,7 @@ export interface UseMutationOptions<
   mutationKey?: MutationKey
   onMutate?: (
     variables: TVariables
-  ) => Promise<TContext> | Promise<undefined> | TContext | undefined
+  ) => Promise<TContext | undefined> | TContext | undefined
   onSuccess?: (
     data: TData,
     variables: TVariables,