diff --git a/src/libosmo-mgcp/mgcp_network.c b/src/libosmo-mgcp/mgcp_network.c
index c85a11d..a73209b 100644
--- a/src/libosmo-mgcp/mgcp_network.c
+++ b/src/libosmo-mgcp/mgcp_network.c
@@ -872,6 +872,22 @@
 {
 	struct mgcp_endpoint *endp;
 	endp = conn->conn->endp;
+	struct sockaddr_in zero_addr = {};
+
+	if (memcmp(&zero_addr, &conn->end.addr, sizeof(zero_addr)) == 0
+	    && conn->conn->mode == MGCP_CONN_LOOPBACK) {
+		/* HACK: for IuUP, we want to reply with an IuUP Initialization ACK upon the first RTP
+		 * message received. We currently hackishly accomplish that by putting the endpoint in
+		 * loopback mode and patching over the looped back RTP message to make it look like an
+		 * ack. We don't know the femto cell's IP address and port until the RAB Assignment
+		 * Response is received, but the nano3G expects an IuUP Initialization Ack before it even
+		 * sends the RAB Assignment Response. Hence, if the remote address is 0.0.0.0 and the
+		 * MGCP port is in loopback mode, allow looping back the packet to any source. */
+		LOGP(DRTP, LOGL_ERROR,
+		     "endpoint:0x%x In loopback mode and remote address not set: allowing data from address: %s\n",
+		     ENDPOINT_NUMBER(endp), inet_ntoa(addr->sin_addr));
+		return 0;
+	}
 
 	/* Note: Check if the inbound RTP data comes from the same host to
 	 * which we send our outgoing RTP traffic. */