diff --git a/scapy/layers/tftp.py b/scapy/layers/tftp.py
index fcd925c3f57..023d1193726 100644
--- a/scapy/layers/tftp.py
+++ b/scapy/layers/tftp.py
@@ -179,7 +179,7 @@ def BEGIN(self):
         self.my_tid = self.sport or RandShort()._fix()
         bind_bottom_up(UDP, TFTP, dport=self.my_tid)
         self.server_tid = None
-        self.res = b""
+        self.res = bytearray()
 
         self.l3 = IP(dst=self.server) / UDP(sport=self.my_tid, dport=self.port) / TFTP()  # noqa: E501
         self.last_packet = self.l3 / TFTP_RRQ(filename=self.filename, mode="octet")  # noqa: E501
@@ -243,7 +243,7 @@ def ERROR(self, pkt):
     @ATMT.state(final=1)
     def END(self):
         split_bottom_up(UDP, TFTP, dport=self.my_tid)
-        return self.res
+        return bytes(self.res)
 
 
 class TFTP_write(Automaton):
diff --git a/test/scapy/layers/tftp.uts b/test/scapy/layers/tftp.uts
index c54e271a08e..756a735d639 100644
--- a/test/scapy/layers/tftp.uts
+++ b/test/scapy/layers/tftp.uts
@@ -70,6 +70,28 @@ tftp_read = TFTP_read("file.txt", "1.2.3.4", sport=0x2807,
 res = tftp_read.run()
 assert res == (b"P" * 512 + b"<3")
 
+= TFTP_read extends one response buffer after the first block
+from scapy.automaton import ATMT
+from scapy.layers.tftp import TFTP_read
+from scapy.packet import Raw
+
+client = object.__new__(TFTP_read)
+client.res = bytearray()
+client.awaiting = 1
+client.blocksize = 512
+
+def receive_full_block():
+    try:
+        TFTP_read.RECEIVING.atmt_origfunc(client, Raw(b"A" * 512))
+    except ATMT.NewStateRequested:
+        pass
+
+receive_full_block()
+receive_full_block()
+response_buffer = client.res
+receive_full_block()
+assert client.res is response_buffer
+
 = TFTP_read() automaton error
 ~ linux