diff --git a/src/cpp/rtps/builtin/discovery/participant/PDPSimple.cpp b/src/cpp/rtps/builtin/discovery/participant/PDPSimple.cpp
index a9e6fb638a3..3c9cf1ff38b 100644
--- a/src/cpp/rtps/builtin/discovery/participant/PDPSimple.cpp
+++ b/src/cpp/rtps/builtin/discovery/participant/PDPSimple.cpp
@@ -309,27 +309,29 @@ bool PDPSimple::createPDPEndpoints()
         secure_endpoints->secure_reader.listener_.reset(new PDPListener(this));
 
         endpoints = secure_endpoints;
-        endpoints->reader.listener_.reset(new PDPSecurityInitiatorListener(this, [this](const ParticipantProxyData& participant_data)
-            {
-                auto secure_pdp_endpoints = static_cast<fastdds::rtps::SimplePDPEndpointsSecure*>(builtin_endpoints_.get());
-                std::lock_guard<fastdds::RecursiveTimedMutex> wlock(secure_pdp_endpoints->writer.writer_->getMutex());
+        endpoints->reader.listener_.reset(new PDPSecurityInitiatorListener(this,
+                [this](const ParticipantProxyData& participant_data)
+                {
+                    auto secure_pdp_endpoints =
+                    static_cast<fastdds::rtps::SimplePDPEndpointsSecure*>(builtin_endpoints_.get());
+                    std::lock_guard<fastdds::RecursiveTimedMutex> wlock(secure_pdp_endpoints->writer.writer_->getMutex());
 
-                CacheChange_t* change = nullptr;
-                secure_pdp_endpoints->writer.history_->get_earliest_change(&change);
+                    CacheChange_t* change = nullptr;
+                    secure_pdp_endpoints->writer.history_->get_earliest_change(&change);
 
-                if (change != nullptr)
-                {
-                    std::vector<GUID_t> remote_readers;
-                    LocatorList_t locators;
+                    if (change != nullptr)
+                    {
+                        std::vector<GUID_t> remote_readers;
+                        LocatorList_t locators;
 
-                    // Send discovery information through the non-secure PDP writer
-                    remote_readers.emplace_back(participant_data.m_guid.guidPrefix, c_EntityId_SPDPReader);
+                        // Send discovery information through the non-secure PDP writer
+                        remote_readers.emplace_back(participant_data.m_guid.guidPrefix, c_EntityId_SPDPReader);
 
-                    fastdds::rtps::FakeWriter writer(getRTPSParticipant(), c_EntityId_SPDPWriter);
+                        fastdds::rtps::FakeWriter writer(getRTPSParticipant(), c_EntityId_SPDPWriter);
 
-                    direct_send(getRTPSParticipant(), locators, remote_readers, *change, writer);
-                }
-            }));
+                        direct_send(getRTPSParticipant(), locators, remote_readers, *change, writer);
+                    }
+                }));
     }
     else
 #endif  // HAVE_SECURITY
diff --git a/test/blackbox/common/BlackboxTestsSecurity.cpp b/test/blackbox/common/BlackboxTestsSecurity.cpp
index a50d1cff811..fcd2e320b54 100644
--- a/test/blackbox/common/BlackboxTestsSecurity.cpp
+++ b/test/blackbox/common/BlackboxTestsSecurity.cpp
@@ -5031,7 +5031,7 @@ TEST(Security, security_with_initial_peers_over_tcpv4_correctly_behaves)
     Locator_t wan_locator;
     IPFinder::getIP4Address(&all_locators);
 
-    for (auto &locator : all_locators)
+    for (auto& locator : all_locators)
     {
         if (!IPLocator::isLocal(locator))
         {
@@ -5048,8 +5048,8 @@ TEST(Security, security_with_initial_peers_over_tcpv4_correctly_behaves)
     LocatorList_t initial_peers;
     initial_peers.push_back(wan_locator);
     tcp_client.disable_builtin_transport()
-              .add_user_transport_to_pparams(tcp_client_transport_descriptor)
-              .initial_peers(initial_peers);
+            .add_user_transport_to_pparams(tcp_client_transport_descriptor)
+            .initial_peers(initial_peers);
 
     auto tcp_server_transport_descriptor = std::make_shared<eprosima::fastdds::rtps::TCPv4TransportDescriptor>();
     tcp_server_transport_descriptor->listening_ports.push_back(server_listening_port);
@@ -5058,7 +5058,7 @@ TEST(Security, security_with_initial_peers_over_tcpv4_correctly_behaves)
     std::cout << "SETTING WAN address to " <<  wan_locator << std::endl;
 
     tcp_server.disable_builtin_transport()
-              .add_user_transport_to_pparams(tcp_server_transport_descriptor);
+            .add_user_transport_to_pparams(tcp_server_transport_descriptor);
 
     // Configure security
     const std::string governance_file("governance_helloworld_all_enable.smime");
@@ -5087,6 +5087,66 @@ TEST(Security, security_with_initial_peers_over_tcpv4_correctly_behaves)
     tcp_server.block_for_all(std::chrono::seconds(10));
 }
 
+//! Regression test for Redmine issue #20181
+TEST(Security, security_with_initial_peers_over_tcpv4_localhost_correctly_behaves)
+{
+    // Create
+    PubSubWriter<HelloWorldPubSubType> tcp_client("HelloWorldTopic_TCPLocalhost");
+    PubSubReader<HelloWorldPubSubType> tcp_server("HelloWorldTopic_TCPLocalhost");
+
+    // Search for a valid WAN address
+    LocatorList_t all_locators;
+    Locator_t wan_locator;
+
+    uint16_t server_listening_port = 11810;
+    wan_locator.port = server_listening_port;
+    wan_locator.kind = LOCATOR_KIND_TCPv4;
+    IPLocator::setIPv4(wan_locator, "127.0.0.1");
+
+    // Need to specify metatraffic locator for localhost
+
+    auto tcp_client_transport_descriptor = std::make_shared<eprosima::fastdds::rtps::TCPv4TransportDescriptor>();
+    LocatorList_t initial_peers;
+    initial_peers.push_back(wan_locator);
+    tcp_client.disable_builtin_transport()
+            .add_user_transport_to_pparams(tcp_client_transport_descriptor)
+            .initial_peers(initial_peers);
+
+    auto tcp_server_transport_descriptor = std::make_shared<eprosima::fastdds::rtps::TCPv4TransportDescriptor>();
+    tcp_server_transport_descriptor->listening_ports.push_back(server_listening_port);
+    IPLocator::copyIPv4(wan_locator, tcp_server_transport_descriptor->wan_addr);
+
+    std::cout << "SETTING WAN address to " <<  wan_locator << std::endl;
+
+    tcp_server.disable_builtin_transport()
+            .add_user_transport_to_pparams(tcp_server_transport_descriptor);
+
+    // Configure security
+    const std::string governance_file("governance_helloworld_all_enable.smime");
+    const std::string permissions_file("permissions_helloworld.smime");
+    CommonPermissionsConfigure(tcp_server, tcp_client, governance_file, permissions_file);
+
+    tcp_server.init();
+    tcp_client.init();
+
+    ASSERT_TRUE(tcp_server.isInitialized());
+    ASSERT_TRUE(tcp_client.isInitialized());
+
+    tcp_server.waitAuthorized();
+    tcp_client.waitAuthorized();
+
+    tcp_server.wait_discovery();
+    tcp_client.wait_discovery();
+
+    ASSERT_TRUE(tcp_server.is_matched());
+    ASSERT_TRUE(tcp_client.is_matched());
+
+    auto data = default_helloworld_data_generator();
+    tcp_server.startReception(data);
+    tcp_client.send(data);
+    ASSERT_TRUE(data.empty());
+    tcp_server.block_for_all();
+}
 
 void blackbox_security_init()
 {