diff --git a/src/errors.ts b/src/errors.ts
index 90d0f03..65a4a15 100644
--- a/src/errors.ts
+++ b/src/errors.ts
@@ -17,4 +17,5 @@ export const gatewayErrors = {
     ALREADY_AUTHENTICATED: { code: 4006, message: "Already authenticated" },
     PAYLOAD_TOO_LARGE: { code: 4007, message: "Payload too large" },
     TOO_MANY_SESSIONS: { code: 4008, message: "Too many sessions" },
+    NOT_AUTHENTICATED: { code: 4009, message: "Not authenticated" },
 };
diff --git a/src/gateway/index.ts b/src/gateway/index.ts
index b70cfd1..99990a0 100644
--- a/src/gateway/index.ts
+++ b/src/gateway/index.ts
@@ -245,6 +245,10 @@ export default function(server: Server) {
                         return closeWithBadPayload(ws, "d: expected numeric '0'");
                     }
 
+                    if (!ws.state.ready) {
+                        return closeWithError(ws, gatewayErrors.NOT_AUTHENTICATED);
+                    }
+
                     // TODO: also check session here
                     ws.state.alive = true;
                     break;