diff --git a/src/treaty2/index.ts b/src/treaty2/index.ts
index fe54d80..d1e4ed0 100644
--- a/src/treaty2/index.ts
+++ b/src/treaty2/index.ts
@@ -292,31 +292,6 @@ const createProxy = (
 
                     if (isGetOrHead) delete fetchInit.body
 
-                    if (onRequest) {
-                        if (!Array.isArray(onRequest)) onRequest = [onRequest]
-
-                        for (const value of onRequest) {
-                            const temp = await value(path, fetchInit)
-
-                            if (typeof temp === 'object')
-                                fetchInit = {
-                                    ...fetchInit,
-                                    ...temp,
-                                    headers: {
-                                        ...fetchInit.headers,
-                                        ...processHeaders(
-                                            temp.headers,
-                                            path,
-                                            fetchInit
-                                        )
-                                    }
-                                }
-                        }
-                    }
-
-                    // ? Duplicate because end-user might add a body in onRequest
-                    if (isGetOrHead) delete fetchInit.body
-
                     if (hasFile(body)) {
                         const formData = new FormData()
 
@@ -396,12 +371,19 @@ const createProxy = (
                                     ...temp,
                                     headers: {
                                         ...fetchInit.headers,
-                                        ...temp.headers
-                                    } as Record<string, string>
+                                        ...processHeaders(
+                                            temp.headers,
+                                            path,
+                                            fetchInit
+                                        )
+                                    }
                                 }
                         }
                     }
 
+                    // ? Duplicate because end-user might add a body in onRequest
+                    if (isGetOrHead) delete fetchInit.body
+
                     const url = domain + path + q
                     const response = await (elysia?.handle(
                         new Request(url, fetchInit)
diff --git a/test/treaty2.test.ts b/test/treaty2.test.ts
index 2b96873..c7c26b1 100644
--- a/test/treaty2.test.ts
+++ b/test/treaty2.test.ts
@@ -3,6 +3,7 @@ import { treaty } from '../src'
 
 import { describe, expect, it, beforeAll, afterAll, mock } from 'bun:test'
 
+
 const randomObject = {
     a: 'a',
     b: 2,
@@ -20,6 +21,7 @@ const randomArray = [
     new Date(0),
     { a: 'a', b: 2, c: true, d: false, e: null, f: new Date(0) }
 ]
+
 const websocketPayloads = [
     // strings
     'str',
@@ -110,6 +112,21 @@ const app = new Elysia()
             })
         }
     )
+    .get(
+        '/headers-uppercased',
+        ({ headers, headers: { username, alias } }) => ({
+            username,
+            alias,
+            authorization: headers.authorization
+        }),
+        {
+            headers: t.Object({
+                username: t.String(),
+                alias: t.Literal('Kristen'),
+                authorization: t.Optional(t.Literal('Bearer token'))
+            })
+        }
+    )
     .get(
         '/headers-custom',
         ({ headers, headers: { username, alias } }) => ({
@@ -341,6 +358,38 @@ describe('Treaty2', () => {
         })
     })
 
+    it('can handle upper case header values', async () => {
+        const client = treaty(app, {
+            onRequest(path) {
+                if (path === '/headers-uppercased') {
+                    return {
+                        headers: {
+                            Authorization: 'Bearer token'
+                        }
+                    }
+                }
+            },
+            async onResponse(response) {
+                return { intercepted: true, data: await response.json() }
+            }
+        })
+
+        const headers = { username: 'a', alias: 'Kristen' } as const
+
+        const { data } = await client['headers-uppercased'].get({
+            headers
+        })
+
+        expect(data).toEqual({
+            // @ts-expect-error
+            intercepted: true,
+            data: {
+                ...headers,
+                authorization: 'Bearer token'
+            }
+        })
+    })
+
     it('handle interception array', async () => {
         const client = treaty(app, {
             onRequest: [