diff --git a/index.d.cts b/index.d.cts
index 918cb08f..c386ae82 100644
--- a/index.d.cts
+++ b/index.d.cts
@@ -629,7 +629,7 @@ declare namespace axios {
 
   interface AxiosInterceptorOptions {
     synchronous?: boolean;
-    runWhen?: (config: InternalAxiosRequestConfig) => boolean;
+    runWhen?: ((config: InternalAxiosRequestConfig) => boolean) | null;
   }
 
   type AxiosInterceptorFulfilled<T> = (value: T) => T | Promise<T>;
@@ -650,7 +650,7 @@ declare namespace axios {
     fulfilled: AxiosInterceptorFulfilled<T>;
     rejected?: AxiosInterceptorRejected;
     synchronous: boolean;
-    runWhen?: (config: AxiosRequestConfig) => boolean;
+    runWhen?: ((config: InternalAxiosRequestConfig) => boolean) | null;
   }
 
   interface AxiosInterceptorManager<V> {
diff --git a/index.d.ts b/index.d.ts
index 300eb7c5..af25bd44 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -639,7 +639,7 @@ export interface CancelTokenSource {
 
 export interface AxiosInterceptorOptions {
   synchronous?: boolean;
-  runWhen?: (config: InternalAxiosRequestConfig) => boolean;
+  runWhen?: ((config: InternalAxiosRequestConfig) => boolean) | null;
 }
 
 type AxiosInterceptorFulfilled<T> = (value: T) => T | Promise<T>;
@@ -660,7 +660,7 @@ interface AxiosInterceptorHandler<T> {
   fulfilled: AxiosInterceptorFulfilled<T>;
   rejected?: AxiosInterceptorRejected;
   synchronous: boolean;
-  runWhen: (config: AxiosRequestConfig) => boolean | null;
+  runWhen?: ((config: InternalAxiosRequestConfig) => boolean) | null;
 }
 
 export interface AxiosInterceptorManager<V> {