diff --git a/Test/Components/DataSources/UDPStreamer/UDPStreamerTest.cpp b/Test/Components/DataSources/UDPStreamer/UDPStreamerTest.cpp
index 279d868..819ff35 100644
--- a/Test/Components/DataSources/UDPStreamer/UDPStreamerTest.cpp
+++ b/Test/Components/DataSources/UDPStreamer/UDPStreamerTest.cpp
@@ -1559,6 +1559,7 @@ bool UDPStreamerTest::TestInitialise_MulticastMode_Valid() {
     ConfigurationDatabase cdb;
     cdb.Write("Port", 44710u);
     cdb.Write("MulticastGroup", "239.0.0.1");
+    cdb.Write("Interface", "127.0.0.1");
     cdb.Write("DataPort", 44711u);
     cdb.CreateRelative("Signals");
     cdb.MoveToRoot();
@@ -1574,6 +1575,7 @@ bool UDPStreamerTest::TestInitialise_MulticastMode_DefaultDataPort() {
     ConfigurationDatabase cdb;
     cdb.Write("Port", 44712u);
     cdb.Write("MulticastGroup", "239.0.0.1");
+    cdb.Write("Interface", "127.0.0.1");
     /* DataPort intentionally omitted: should default to 44713 */
     cdb.CreateRelative("Signals");
     cdb.MoveToRoot();
@@ -1588,6 +1590,9 @@ bool UDPStreamerTest::TestInitialise_MulticastMode_InvalidDataPort() {
     ConfigurationDatabase cdb;
     cdb.Write("Port", 44714u);
     cdb.Write("MulticastGroup", "239.0.0.1");
+    /* Interface is mandatory for multicast; supply it so the rejection below
+     * is provably caused by DataPort == Port and not by a missing Interface. */
+    cdb.Write("Interface", "127.0.0.1");
     cdb.Write("DataPort", 44714u); /* same as Port — must be rejected */
     cdb.CreateRelative("Signals");
     cdb.MoveToRoot();
@@ -1618,6 +1623,7 @@ bool UDPStreamerTest::TestPrepareNextState_Multicast() {
         "            Class = UDPStreamer\n"
         "            Port = 44716\n"
         "            MulticastGroup = \"239.0.0.1\"\n"
+        "            Interface = \"127.0.0.1\"\n"
         "            DataPort = 44717\n"
         "            MaxPayloadSize = 1400\n"
         "            Signals = {\n"
@@ -1695,6 +1701,7 @@ bool UDPStreamerTest::TestExecute_MulticastConnectDataDisconnect() {
         "            Class = UDPStreamer\n"
         "            Port = 44720\n"
         "            MulticastGroup = \"239.0.0.1\"\n"
+        "            Interface = \"127.0.0.1\"\n"
         "            DataPort = 44721\n"
         "            MaxPayloadSize = 1400\n"
         "            Signals = {\n"
@@ -1786,7 +1793,12 @@ bool UDPStreamerTest::TestExecute_MulticastConnectDataDisconnect() {
         ok = mcastReader.Listen(44721u);
     }
     if (ok) {
-        ok = mcastReader.Join("239.0.0.1");
+        /* Join on the same interface the streamer sends from (Interface =
+         * 127.0.0.1 sets IP_MULTICAST_IF on the server's data socket). The
+         * single-argument Join() would pass INADDR_ANY, letting the kernel
+         * pick the default-route interface, and the datagram would never
+         * reach this socket. */
+        ok = mcastReader.Join("239.0.0.1", "127.0.0.1");
     }
 
     /* Step 4: Trigger Synchronise() to generate a DATA packet */