diff --git a/packages/safe-chain/src/registryProxy/interceptors/interceptorBuilder.js b/packages/safe-chain/src/registryProxy/interceptors/interceptorBuilder.js
index 003aae7..e25e641 100644
--- a/packages/safe-chain/src/registryProxy/interceptors/interceptorBuilder.js
+++ b/packages/safe-chain/src/registryProxy/interceptors/interceptorBuilder.js
@@ -10,14 +10,14 @@ import { EventEmitter } from "events";
  * @typedef {Object} RequestInterceptionContext
  * @property {string} targetUrl
  * @property {(packageName: string | undefined, version: string | undefined) => void} blockMalware
- * @property {(modificationFunc: (headers: NodeJS.Dict<string | string[]>) => void) => void} modifyRequestHeaders
+ * @property {(modificationFunc: (headers: NodeJS.Dict<string | string[]>) => NodeJS.Dict<string | string[]>) => void} modifyRequestHeaders
  * @property {(modificationFunc: (body: Buffer, headers: NodeJS.Dict<string | string[]> | undefined) => Buffer) => void} modifyBody
  * @property {() => RequestInterceptionHandler} build
  *
  *
  * @typedef {Object} RequestInterceptionHandler
  * @property {{statusCode: number, message: string} | undefined} blockResponse
- * @property {(headers: NodeJS.Dict<string | string[]> | undefined) => void} modifyRequestHeaders
+ * @property {(headers: NodeJS.Dict<string | string[]> | undefined) => NodeJS.Dict<string | string[]> | undefined} modifyRequestHeaders
  * @property {() => boolean} modifiesResponse
  * @property {(body: Buffer, headers: NodeJS.Dict<string | string[]> | undefined) => Buffer} modifyBody
  */
@@ -65,7 +65,7 @@ function buildInterceptor(requestHandlers) {
 function createRequestContext(targetUrl, eventEmitter) {
   /** @type {{statusCode: number, message: string} | undefined}  */
   let blockResponse = undefined;
-  /** @type {Array<(headers: NodeJS.Dict<string | string[]>) => void>} */
+  /** @type {Array<(headers: NodeJS.Dict<string | string[]>) => NodeJS.Dict<string | string[]>>} */
   let reqheaderModificationFuncs = [];
   /** @type {Array<(body: Buffer, headers: NodeJS.Dict<string | string[]> | undefined) => Buffer>} */
   let modifyBodyFuncs = [];
@@ -91,13 +91,18 @@ function createRequestContext(targetUrl, eventEmitter) {
 
   /** @returns {RequestInterceptionHandler} */
   function build() {
-    /** @param {NodeJS.Dict<string | string[]> | undefined} headers */
+    /**
+     * @param {NodeJS.Dict<string | string[]> | undefined} headers
+     * @returns {NodeJS.Dict<string | string[]> | undefined}
+     */
     function modifyRequestHeaders(headers) {
-      if (!headers) return;
-
-      for (const func of reqheaderModificationFuncs) {
-        func(headers);
+      if (headers) {
+        for (const func of reqheaderModificationFuncs) {
+          func(headers);
+        }
       }
+
+      return headers;
     }
 
     /**
diff --git a/packages/safe-chain/src/registryProxy/interceptors/npm/modifyNpmInfo.js b/packages/safe-chain/src/registryProxy/interceptors/npm/modifyNpmInfo.js
index 0e7e41d..47c63d0 100644
--- a/packages/safe-chain/src/registryProxy/interceptors/npm/modifyNpmInfo.js
+++ b/packages/safe-chain/src/registryProxy/interceptors/npm/modifyNpmInfo.js
@@ -8,6 +8,7 @@ const state = {
 
 /**
  * @param {NodeJS.Dict<string | string[]>} headers
+ * @returns {NodeJS.Dict<string | string[]>}
  */
 export function modifyNpmInfoRequestHeaders(headers) {
   const accept = getHeaderValueAsString(headers, "accept");
@@ -17,6 +18,7 @@ export function modifyNpmInfoRequestHeaders(headers) {
     // Force the registry to return the full metadata by changing the Accept header.
     headers["accept"] = "application/json";
   }
+  return headers;
 }
 
 /**
diff --git a/packages/safe-chain/src/registryProxy/mitmRequestHandler.js b/packages/safe-chain/src/registryProxy/mitmRequestHandler.js
index 9afadaa..9845cd2 100644
--- a/packages/safe-chain/src/registryProxy/mitmRequestHandler.js
+++ b/packages/safe-chain/src/registryProxy/mitmRequestHandler.js
@@ -151,11 +151,12 @@ function forwardRequest(req, hostname, res, requestHandler) {
  * @returns {import("http").ClientRequest}
  */
 function createProxyRequest(hostname, req, res, requestHandler) {
-  const headers = { ...req.headers };
+  /** @type {NodeJS.Dict<string | string[]> | undefined} */
+  let headers = { ...req.headers };
   if (headers.host) {
     delete headers.host;
   }
-  requestHandler.modifyRequestHeaders(headers);
+  headers = requestHandler.modifyRequestHeaders(headers);
 
   /** @type {import("http").RequestOptions} */
   const options = {