diff --git a/src/hw/hw_vdf_client.cpp b/src/hw/hw_vdf_client.cpp
index 19d063dd..24a98469 100644
--- a/src/hw/hw_vdf_client.cpp
+++ b/src/hw/hw_vdf_client.cpp
@@ -127,7 +127,7 @@ void clear_vdf_client(struct vdf_client *client)
 void stop_conn(struct vdf_client *client, struct vdf_conn *conn)
 {
     if (conn->sock >= 0) {
-        write_data(conn, "STOP", 4);
+        write_data(conn, "\0\0\0\0", 4);
     }
     if (conn->vdf.init_done) {
         hw_stop_proof(&conn->vdf);
diff --git a/src/tl_emu.py b/src/tl_emu.py
index e707a37f..35965f36 100644
--- a/src/tl_emu.py
+++ b/src/tl_emu.py
@@ -24,7 +24,7 @@
 # proof for witness type=0: proof value (100 bytes as compressed form)
 
 # VDF client -> Timelord
-# "STOP"
+# 0-length
 
 # Timelord -> VDF client
 # "ACK"
@@ -68,7 +68,8 @@ async def read_conn(reader, writer, d, idx, task):
     try:
         while True:
             data = await reader.read(4)
-            if data == b"STOP":
+            size = int.from_bytes(data, 'big')
+            if size == 0:
                 await send_msg(writer, b"ACK")
                 print("Closing connection for VDF %d" % (idx,))
                 clear_conn_idx(idx)
@@ -76,10 +77,6 @@ async def read_conn(reader, writer, d, idx, task):
                 task.cancel()
                 break
 
-            size = int.from_bytes(data, 'big')
-            if not size:
-                raise ValueError("Empty proof!")
-
             data = await reader.readexactly(size)
             data = bytes.fromhex(data.decode())
             iters = int.from_bytes(data[:8], 'big')
diff --git a/src/vdf_client.cpp b/src/vdf_client.cpp
index f22badc6..cbeca489 100644
--- a/src/vdf_client.cpp
+++ b/src/vdf_client.cpp
@@ -119,7 +119,7 @@ void FinishSession(tcp::socket& sock) {
         PrintInfo("Stopped everything! Ready for the next challenge.");
 
         std::lock_guard<std::mutex> lock(socket_mutex);
-        boost::asio::write(sock, boost::asio::buffer("STOP", 4));
+        boost::asio::write(sock, boost::asio::buffer("\0\0\0\0", 4));
 
         char ack[5];
         memset(ack, 0x00, sizeof(ack));