diff --git a/browse/src/token-registry.ts b/browse/src/token-registry.ts
index 89b0a990c..b241e55e4 100644
--- a/browse/src/token-registry.ts
+++ b/browse/src/token-registry.ts
@@ -377,7 +377,9 @@ export function exchangeSetupKey(setupKey: string, sessionExpiresSeconds?: numbe
 
 /**
  * Validate a token and return its info if valid.
- * Returns null for expired, revoked, or unknown tokens.
+ * Returns null for expired, revoked, or unknown tokens, and for unexchanged
+ * setup keys: a setup key authenticates only the /connect exchange, never a
+ * bearer request.
  * Root token returns a special root info object.
  */
 export function validateToken(token: string): TokenInfo | null {
@@ -396,7 +398,7 @@ export function validateToken(token: string): TokenInfo | null {
   }
 
   const info = tokens.get(token);
-  if (!info) return null;
+  if (!info || info.type !== 'session') return null;
 
   // Check expiry
   if (info.expiresAt && new Date(info.expiresAt) < new Date()) {
diff --git a/browse/test/token-registry.test.ts b/browse/test/token-registry.test.ts
index 3d2639b83..77b665f74 100644
--- a/browse/test/token-registry.test.ts
+++ b/browse/test/token-registry.test.ts
@@ -233,15 +233,19 @@ describe('token-registry', () => {
 
     it('rejects expired setup key', () => {
       const setup = createSetupKey({});
-      // Manually expire it
-      const info = validateToken(setup.token);
-      if (info) {
-        (info as any).expiresAt = new Date(Date.now() - 1000).toISOString();
-      }
+      // Manually expire it (createSetupKey returns the registry's own record)
+      setup.expiresAt = new Date(Date.now() - 1000).toISOString();
       const session = exchangeSetupKey(setup.token);
       expect(session).toBeNull();
     });
 
+    it('does not accept an unexchanged setup key as a bearer token', () => {
+      const setup = createSetupKey({ scopes: ['read', 'write'] });
+      expect(validateToken(setup.token)).toBeNull();
+      const session = exchangeSetupKey(setup.token);
+      expect(validateToken(session!.token)).not.toBeNull();
+    });
+
     it('rejects unknown setup key', () => {
       expect(exchangeSetupKey('gsk_setup_nonexistent')).toBeNull();
     });