diff --git a/pkg/packet/rtr/rtr.go b/pkg/packet/rtr/rtr.go
index 59755b781..b1a768277 100644
--- a/pkg/packet/rtr/rtr.go
+++ b/pkg/packet/rtr/rtr.go
@@ -41,15 +41,17 @@ const (
 )
 
 const (
-	RTR_SERIAL_NOTIFY_LEN         = 12
-	RTR_SERIAL_QUERY_LEN          = 12
-	RTR_RESET_QUERY_LEN           = 8
-	RTR_CACHE_RESPONSE_LEN        = 8
-	RTR_IPV4_PREFIX_LEN           = 20
-	RTR_IPV6_PREFIX_LEN           = 32
-	RTR_END_OF_DATA_LEN           = 12
-	RTR_CACHE_RESET_LEN           = 8
-	RTR_MIN_LEN                   = 8
+	RTR_SERIAL_NOTIFY_LEN  = 12
+	RTR_SERIAL_QUERY_LEN   = 12
+	RTR_RESET_QUERY_LEN    = 8
+	RTR_CACHE_RESPONSE_LEN = 8
+	RTR_IPV4_PREFIX_LEN    = 20
+	RTR_IPV6_PREFIX_LEN    = 32
+	RTR_END_OF_DATA_LEN    = 12
+	RTR_CACHE_RESET_LEN    = 8
+	RTR_MIN_LEN            = 8
+	// RTR_MAX_LEN caps the on-wire Length; every defined PDU is far smaller.
+	RTR_MAX_LEN                   = 65535
 	RTR_ERROR_REPORT_ERR_PDU_LEN  = 4
 	RTR_ERROR_REPORT_ERR_TEXT_LEN = 4
 )
diff --git a/pkg/server/rpki.go b/pkg/server/rpki.go
index f137e4430..f2edb7afa 100644
--- a/pkg/server/rpki.go
+++ b/pkg/server/rpki.go
@@ -444,25 +444,38 @@ func (c *roaClient) established() (err error) {
 	}
 
 	for {
-		header := make([]byte, rtr.RTR_MIN_LEN)
-		if _, err = io.ReadFull(c.conn, header); err != nil {
-			return err
-		}
-		totalLen := binary.BigEndian.Uint32(header[4:8])
-		if totalLen < rtr.RTR_MIN_LEN {
-			return fmt.Errorf("too short header length %v", totalLen)
-		}
-
-		body := make([]byte, totalLen-rtr.RTR_MIN_LEN)
-		if _, err = io.ReadFull(c.conn, body); err != nil {
+		var data []byte
+		data, err = readRTRMessage(c.conn)
+		if err != nil {
 			return err
 		}
 
 		c.eventCh <- &roaEvent{
 			EventType: roaRTR,
 			Src:       c.host,
-			Data:      append(header, body...),
+			Data:      data,
 			timestamp: time.Now(),
 		}
 	}
 }
+
+func readRTRMessage(r io.Reader) ([]byte, error) {
+	header := make([]byte, rtr.RTR_MIN_LEN)
+	if _, err := io.ReadFull(r, header); err != nil {
+		return nil, err
+	}
+	totalLen := binary.BigEndian.Uint32(header[4:8])
+	if totalLen < rtr.RTR_MIN_LEN {
+		return nil, fmt.Errorf("too short header length %v", totalLen)
+	}
+	if totalLen > rtr.RTR_MAX_LEN {
+		return nil, fmt.Errorf("too large header length %v", totalLen)
+	}
+
+	body := make([]byte, totalLen-rtr.RTR_MIN_LEN)
+	if _, err := io.ReadFull(r, body); err != nil {
+		return nil, err
+	}
+
+	return append(header, body...), nil
+}
diff --git a/pkg/server/rpki_test.go b/pkg/server/rpki_test.go
new file mode 100644
index 000000000..8371b8698
--- /dev/null
+++ b/pkg/server/rpki_test.go
@@ -0,0 +1,50 @@
+// Copyright (C) 2015-2021 Nippon Telegraph and Telephone Corporation.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+// implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package server
+
+import (
+	"bytes"
+	"encoding/binary"
+	"testing"
+
+	"github.com/osrg/gobgp/v4/pkg/packet/rtr"
+)
+
+func Test_readRTRMessageRejectsOversizedLength(t *testing.T) {
+	header := make([]byte, rtr.RTR_MIN_LEN)
+	header[0] = 1 // Protocol Version
+	header[1] = rtr.RTR_CACHE_RESET
+	binary.BigEndian.PutUint32(header[4:8], 0xffffffff)
+
+	if _, err := readRTRMessage(bytes.NewReader(header)); err == nil {
+		t.Fatal("expected an error for an oversized RTR Length, got nil")
+	}
+}
+
+func Test_readRTRMessageAcceptsValidLength(t *testing.T) {
+	header := make([]byte, rtr.RTR_MIN_LEN)
+	header[0] = 1 // Protocol Version
+	header[1] = rtr.RTR_CACHE_RESET
+	binary.BigEndian.PutUint32(header[4:8], rtr.RTR_MIN_LEN)
+
+	data, err := readRTRMessage(bytes.NewReader(header))
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if len(data) != rtr.RTR_MIN_LEN {
+		t.Fatalf("expected %d bytes, got %d", rtr.RTR_MIN_LEN, len(data))
+	}
+}