diff --git a/.changeset/sharp-eggs-remember.md b/.changeset/sharp-eggs-remember.md
new file mode 100644
index 0000000000..b38333b4d8
--- /dev/null
+++ b/.changeset/sharp-eggs-remember.md
@@ -0,0 +1,5 @@
+---
+'@shopify/theme': patch
+---
+
+Fix cart/add request in development.
diff --git a/packages/theme/src/cli/utilities/theme-environment/proxy.test.ts b/packages/theme/src/cli/utilities/theme-environment/proxy.test.ts
index 3f01315cfc..d6e9ba9550 100644
--- a/packages/theme/src/cli/utilities/theme-environment/proxy.test.ts
+++ b/packages/theme/src/cli/utilities/theme-environment/proxy.test.ts
@@ -180,9 +180,9 @@ describe('dev proxy', () => {
       // Removed:
       event.node.req.headers.connection = '...'
       event.node.req.headers['proxy-authenticate'] = '...'
-      event.node.req.headers.accept = 'text/html'
       event.node.req.headers.host = 'abnb'
       // Kept:
+      event.node.req.headers.accept = 'text/html'
       event.node.req.headers.cookie = 'oreo'
       event.node.req.headers['user-agent'] = 'vitest'
       event.node.req.headers['x-custom'] = 'true'
@@ -190,6 +190,7 @@ describe('dev proxy', () => {
       expect(getProxyStorefrontHeaders(event)).toMatchInlineSnapshot(`
         {
           "X-Forwarded-For": "42",
+          "accept": "text/html",
           "cookie": "oreo",
           "user-agent": "vitest",
           "x-custom": "true",
diff --git a/packages/theme/src/cli/utilities/theme-environment/proxy.ts b/packages/theme/src/cli/utilities/theme-environment/proxy.ts
index 619411574f..4387ce0e48 100644
--- a/packages/theme/src/cli/utilities/theme-environment/proxy.ts
+++ b/packages/theme/src/cli/utilities/theme-environment/proxy.ts
@@ -4,7 +4,7 @@ import {
   defineEventHandler,
   clearResponseHeaders,
   sendProxy,
-  getProxyRequestHeaders,
+  getRequestHeaders,
   getRequestWebStream,
   getRequestIP,
   type H3Event,
@@ -167,7 +167,9 @@ const HOP_BY_HOP_HEADERS = [
   'trailer',
   'transfer-encoding',
   'upgrade',
+  'expect',
   'content-security-policy',
+  'host',
 ]
 
 function patchProxiedResponseHeaders(ctx: DevServerContext, event: H3Event, response: Response | NodeResponse) {
@@ -203,10 +205,8 @@ function patchProxiedResponseHeaders(ctx: DevServerContext, event: H3Event, resp
  * Filters headers to forward to SFR.
  */
 export function getProxyStorefrontHeaders(event: H3Event) {
-  const proxyRequestHeaders = getProxyRequestHeaders(event) as {[key: string]: string}
+  const proxyRequestHeaders = getRequestHeaders(event) as {[key: string]: string}
 
-  // H3 already removes most hop-by-hop request headers:
-  // https://github.com/unjs/h3/blob/ac6d83de2abe5411d4eaea8ecf2165ace16a65f3/src/utils/proxy.ts#L25
   for (const headerKey of HOP_BY_HOP_HEADERS) {
     delete proxyRequestHeaders[headerKey]
   }