diff --git a/src/algorithms/telemetry_decoder/gnuradio_blocks/galileo_telemetry_decoder_gs.cc b/src/algorithms/telemetry_decoder/gnuradio_blocks/galileo_telemetry_decoder_gs.cc
index a94aebcf8..b73690f0e 100644
--- a/src/algorithms/telemetry_decoder/gnuradio_blocks/galileo_telemetry_decoder_gs.cc
+++ b/src/algorithms/telemetry_decoder/gnuradio_blocks/galileo_telemetry_decoder_gs.cc
@@ -664,6 +664,7 @@ int galileo_telemetry_decoder_gs::general_work(int noutput_items __attribute__((
                                 d_CRC_error_counter = 0;
                                 d_flag_preamble = true;               // valid preamble indicator (initialized to false every work())
                                 d_preamble_index = d_sample_counter;  // record the preamble sample stamp (t_P)
+                                gr::thread::scoped_lock lock(d_setlock);
                                 d_last_valid_preamble = d_sample_counter;
                                 if (!d_flag_frame_sync)
                                     {