diff --git a/src/algorithms/signal_source/gnuradio_blocks/gr_complex_ip_packet_source.cc b/src/algorithms/signal_source/gnuradio_blocks/gr_complex_ip_packet_source.cc
index d5659d0dc..ae557e2d6 100644
--- a/src/algorithms/signal_source/gnuradio_blocks/gr_complex_ip_packet_source.cc
+++ b/src/algorithms/signal_source/gnuradio_blocks/gr_complex_ip_packet_source.cc
@@ -164,6 +164,7 @@ bool Gr_Complex_Ip_Packet_Source::start()
     // open the ethernet device
     if (open() == true)
         {
+            gr::thread::scoped_lock guard(d_setlock);
             // start pcap capture thread
             d_pcap_thread = new boost::thread(
 #if HAS_GENERIC_LAMBDA
@@ -181,6 +182,7 @@ bool Gr_Complex_Ip_Packet_Source::start()
 bool Gr_Complex_Ip_Packet_Source::stop()
 {
     std::cout << "gr_complex_ip_packet_source STOP\n";
+    gr::thread::scoped_lock guard(d_setlock);
     if (descr != nullptr)
         {
             pcap_breakloop(descr);
@@ -294,11 +296,11 @@ void Gr_Complex_Ip_Packet_Source::pcap_callback(__attribute__((unused)) u_char *
                     const u_char *udp_payload = (reinterpret_cast<const u_char *>(uh) + sizeof(gr_udp_header));
                     if (fifo_items <= (FIFO_SIZE - payload_length_bytes))
                         {
+                            gr::thread::scoped_lock guard(d_setlock);
                             int aligned_write_items = FIFO_SIZE - fifo_write_ptr;
                             if (aligned_write_items >= payload_length_bytes)
                                 {
                                     // write all in a single memcpy
-                                    gr::thread::scoped_lock guard(d_setlock);
                                     memcpy(&fifo_buff[fifo_write_ptr], &udp_payload[0], payload_length_bytes);  // size in bytes
                                     fifo_write_ptr += payload_length_bytes;
                                     if (fifo_write_ptr == FIFO_SIZE)
@@ -310,7 +312,6 @@ void Gr_Complex_Ip_Packet_Source::pcap_callback(__attribute__((unused)) u_char *
                             else
                                 {
                                     // two step wrap write
-                                    gr::thread::scoped_lock guard(d_setlock);
                                     memcpy(&fifo_buff[fifo_write_ptr], &udp_payload[0], aligned_write_items);  // size in bytes
                                     fifo_write_ptr = payload_length_bytes - aligned_write_items;
                                     memcpy(&fifo_buff[0], &udp_payload[aligned_write_items], fifo_write_ptr);  // size in bytes