diff --git a/src/client/auth.test.ts b/src/client/auth.test.ts
index c38f1933..f2dadbb1 100644
--- a/src/client/auth.test.ts
+++ b/src/client/auth.test.ts
@@ -863,7 +863,8 @@ describe('OAuth Authorization', () => {
             const calls = mockFetch.mock.calls;
             const [, options] = calls[0];
             expect(options.headers).toEqual({
-                'MCP-Protocol-Version': '2025-01-01'
+                'MCP-Protocol-Version': '2025-01-01',
+                Accept: 'application/json'
             });
         });
 
diff --git a/src/client/auth.ts b/src/client/auth.ts
index 3c04f7cb..1e90f34b 100644
--- a/src/client/auth.ts
+++ b/src/client/auth.ts
@@ -738,7 +738,10 @@ export async function discoverAuthorizationServerMetadata(
         protocolVersion?: string;
     } = {}
 ): Promise<AuthorizationServerMetadata | undefined> {
-    const headers = { 'MCP-Protocol-Version': protocolVersion };
+    const headers = {
+        'MCP-Protocol-Version': protocolVersion,
+        Accept: 'application/json'
+    };
 
     // Get the list of URLs to try
     const urlsToTry = buildDiscoveryUrls(authorizationServerUrl);