diff --git a/td/mtproto/SessionConnection.cpp b/td/mtproto/SessionConnection.cpp
index 2c4b48687..039660f7a 100644
--- a/td/mtproto/SessionConnection.cpp
+++ b/td/mtproto/SessionConnection.cpp
@@ -662,6 +662,7 @@ bool SessionConnection::must_flush_packet() {
 }
 
 Status SessionConnection::before_write() {
+  CHECK(raw_connection_);
   while (must_flush_packet()) {
     flush_packet();
   }
@@ -715,12 +716,14 @@ void SessionConnection::on_read(size_t size) {
 
 SessionConnection::SessionConnection(Mode mode, unique_ptr<RawConnection> raw_connection, AuthData *auth_data)
     : raw_connection_(std::move(raw_connection)), auth_data_(auth_data) {
+  CHECK(raw_connection_);
   state_ = Init;
   mode_ = mode;
   created_at_ = Time::now();
 }
 
 PollableFdInfo &SessionConnection::get_poll_info() {
+  CHECK(raw_connection_);
   return raw_connection_->get_poll_info();
 }