diff --git a/connect/webConn.go b/connect/webConn.go
index 73629bac6463aedc79c0f4521392535a011b8b6c..cb1610b262b4e0e4e5a23165d98efb00a2534835 100644
--- a/connect/webConn.go
+++ b/connect/webConn.go
@@ -206,6 +206,7 @@ func (wc *webConn) isOnlineHelper(addr string, pingTimeout time.Duration) (time.
 	}
 	target := "https://" + addr + "/mixmessages.Gateway/RequestTlsCert"
 	req, err := http.NewRequest("POST", target, nil)
+	req.Header.Add("content-type", "application/grpc-web+proto")
 	if err != nil {
 		jww.WARN.Printf("Failed to initiate request: %+v", err)
 		return time.Since(start), false