diff --git a/src/lib/functions/registry.mjs b/src/lib/functions/registry.mjs
index 788f7ea0414..fb1b5040026 100644
--- a/src/lib/functions/registry.mjs
+++ b/src/lib/functions/registry.mjs
@@ -24,7 +24,7 @@ import { getPathInProject } from '../settings.mjs'
 import NetlifyFunction from './netlify-function.mjs'
 import runtimes from './runtimes/index.mjs'
 
-const DEFAULT_URL_EXPRESSION = /^\/.netlify\/(functions|builders)\/([^/]+).*/
+export const DEFAULT_FUNCTION_URL_EXPRESSION = /^\/.netlify\/(functions|builders)\/([^/]+).*/
 const TYPES_PACKAGE = '@netlify/functions'
 const ZIP_EXTENSION = '.zip'
 
@@ -238,7 +238,7 @@ export class FunctionsRegistry {
     // the incoming URL. It doesn't really matter that we don't have the actual
     // local URL with the correct port.
     const urlPath = new URL(url, 'http://localhost').pathname
-    const defaultURLMatch = urlPath.match(DEFAULT_URL_EXPRESSION)
+    const defaultURLMatch = urlPath.match(DEFAULT_FUNCTION_URL_EXPRESSION)
 
     if (defaultURLMatch) {
       const func = this.get(defaultURLMatch[2])
diff --git a/src/utils/proxy.mjs b/src/utils/proxy.mjs
index cbf20a17afc..e04df689fab 100644
--- a/src/utils/proxy.mjs
+++ b/src/utils/proxy.mjs
@@ -27,6 +27,7 @@ import {
   isEdgeFunctionsRequest,
 } from '../lib/edge-functions/proxy.mjs'
 import { fileExistsAsync, isFileAsync } from '../lib/fs.mjs'
+import { DEFAULT_FUNCTION_URL_EXPRESSION } from '../lib/functions/registry.mjs'
 import renderErrorTemplate from '../lib/render-error-template.mjs'
 
 import { NETLIFYDEVLOG, NETLIFYDEVWARN, log, chalk } from './command-helpers.mjs'
@@ -87,7 +88,7 @@ function isInternal(url) {
  * @param {string} url
  */
 function isFunction(functionsPort, url) {
-  return functionsPort && url.match(/^\/.netlify\/(functions|builders)\/.+/)
+  return functionsPort && url.match(DEFAULT_FUNCTION_URL_EXPRESSION)
 }
 
 /**
@@ -328,13 +329,12 @@ const serveRedirect = async function ({ env, functionsRegistry, match, options,
       return proxy.web(req, res, { target: options.functionsServer })
     }
 
-    const functionWithCustomRoute =
-      functionsRegistry && (await functionsRegistry.getFunctionForURLPath(destURL, req.method))
+    const matchingFunction = functionsRegistry && (await functionsRegistry.getFunctionForURLPath(destURL, req.method))
     const destStaticFile = await getStatic(dest.pathname, options.publicFolder)
     let statusValue
     if (
       match.force ||
-      (!staticFile && ((!options.framework && destStaticFile) || isInternal(destURL) || functionWithCustomRoute))
+      (!staticFile && ((!options.framework && destStaticFile) || isInternal(destURL) || matchingFunction))
     ) {
       req.url = destStaticFile ? destStaticFile + dest.search : destURL
       const { status } = match
@@ -342,10 +342,11 @@ const serveRedirect = async function ({ env, functionsRegistry, match, options,
       console.log(`${NETLIFYDEVLOG} Rewrote URL to`, req.url)
     }
 
-    if (isFunction(options.functionsPort, req.url) || functionWithCustomRoute) {
-      const functionHeaders = functionWithCustomRoute
-        ? { [NFFunctionName]: functionWithCustomRoute.func.name, [NFFunctionRoute]: functionWithCustomRoute.route }
-        : {}
+    if (matchingFunction) {
+      const functionHeaders = {
+        [NFFunctionName]: matchingFunction.func.name,
+        [NFFunctionRoute]: matchingFunction.route,
+      }
       const url = reqToURL(req, originalURL)
       req.headers['x-netlify-original-pathname'] = url.pathname
       req.headers['x-netlify-original-search'] = url.search