diff --git a/server-packet.go b/server-packet.go
index 1347d43..6d4f65b 100644
--- a/server-packet.go
+++ b/server-packet.go
@@ -46,6 +46,9 @@ type PacketServer struct {
 	// This should only be set to true for debugging purposes.
 	InsecureSkipVerify bool
 
+	// Don't block dupplicated requests (retransmissions).
+	AllowRetransmission bool
+
 	// ErrorLog specifies an optional logger for errors
 	// around packet accepting, processing, and validation.
 	// If nil, logging is done via the log package's standard logger.
@@ -167,30 +170,31 @@ func (s *PacketServer) Serve(conn net.PacketConn) error {
 				return
 			}
 
-			key := requestKey{
-				IP:         remoteAddr.String(),
-				Identifier: packet.Identifier,
-			}
-
-			requestsLock.Lock()
-			if _, ok := requests[key]; ok {
+			if !s.AllowRetransmission {
+				key := requestKey{
+					IP:         remoteAddr.String(),
+					Identifier: packet.Identifier,
+				}
+				requestsLock.Lock()
+				if _, ok := requests[key]; ok {
+					requestsLock.Unlock()
+					return
+				}
+				requests[key] = struct{}{}
 				requestsLock.Unlock()
-				return
-			}
-			requests[key] = struct{}{}
-			requestsLock.Unlock()
 
+				//clean up afterwards
+				defer func() {
+					requestsLock.Lock()
+					delete(requests, key)
+					requestsLock.Unlock()
+				}()
+			}
 			response := packetResponseWriter{
 				conn: conn,
 				addr: remoteAddr,
 			}
 
-			defer func() {
-				requestsLock.Lock()
-				delete(requests, key)
-				requestsLock.Unlock()
-			}()
-
 			request := Request{
 				LocalAddr:  conn.LocalAddr(),
 				RemoteAddr: remoteAddr,
diff --git a/server-packet_test.go b/server-packet_test.go
index 7497aaa..440234c 100644
--- a/server-packet_test.go
+++ b/server-packet_test.go
@@ -186,3 +186,116 @@ func TestPacketServer_singleUse(t *testing.T) {
 		t.Fatalf("got err %v; expecting ErrServerShutdown", err)
 	}
 }
+
+func TestPacketServer_AllowRetransmission(t *testing.T) {
+	addr, err := net.ResolveUDPAddr("udp", "localhost:0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	pc, err := net.ListenUDP("udp", addr)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	secret := []byte("123456790")
+	var receivedRequests = 0
+	var identifiers = make(map[byte]struct{})
+	server := PacketServer{
+		SecretSource:        StaticSecretSource(secret),
+		AllowRetransmission: true,
+		Handler: HandlerFunc(func(w ResponseWriter, r *Request) {
+			receivedRequests++
+			if _, ok := identifiers[r.Identifier]; ok {
+				return
+			}
+			identifiers[r.Identifier] = struct{}{}
+			time.Sleep(time.Millisecond * 200)
+			w.Write(r.Response(CodeAccessReject))
+		}),
+	}
+
+	var clientErr error
+	go func(rr int) {
+		defer server.Shutdown(context.Background())
+
+		packet := New(CodeAccessRequest, secret)
+		client := Client{
+			Retry: time.Millisecond * 10,
+		}
+		response, err := client.Exchange(context.Background(), packet, pc.LocalAddr().String())
+		if err != nil {
+			clientErr = err
+			return
+		}
+		if response.Code != CodeAccessReject {
+			clientErr = fmt.Errorf("got response code %v; expecting CodeAccessReject", response.Code)
+		}
+		if receivedRequests < 2 {
+			clientErr = fmt.Errorf("got %d requests; expecting at least 2", receivedRequests)
+		}
+	}(receivedRequests)
+
+	if err := server.Serve(pc); err != ErrServerShutdown {
+		t.Fatal(err)
+	}
+
+	server.Shutdown(context.Background())
+	if clientErr != nil {
+		t.Fatal(clientErr)
+	}
+}
+
+func TestPacketServer_BlockRetransmission(t *testing.T) {
+	addr, err := net.ResolveUDPAddr("udp", "localhost:0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	pc, err := net.ListenUDP("udp", addr)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var receivedRequests = 0
+	var identifiers = make(map[byte]struct{})
+	secret := []byte("123456790")
+	server := PacketServer{
+		SecretSource: StaticSecretSource(secret),
+		Handler: HandlerFunc(func(w ResponseWriter, r *Request) {
+			receivedRequests++
+			if _, ok := identifiers[r.Identifier]; ok {
+				return
+			}
+			time.Sleep(time.Millisecond * 500)
+			w.Write(r.Response(CodeAccessReject))
+		}),
+	}
+
+	var clientErr error
+	go func(rr int) {
+		defer server.Shutdown(context.Background())
+
+		packet := New(CodeAccessRequest, secret)
+		client := Client{
+			Retry: time.Millisecond * 10,
+		}
+		response, err := client.Exchange(context.Background(), packet, pc.LocalAddr().String())
+		if err != nil {
+			clientErr = err
+			return
+		}
+		if response.Code != CodeAccessReject {
+			clientErr = fmt.Errorf("got response code %v; expecting CodeAccessReject", response.Code)
+		}
+		if receivedRequests != 1 {
+			clientErr = fmt.Errorf("got %d requests; expecting only 1", receivedRequests)
+		}
+	}(receivedRequests)
+
+	if err := server.Serve(pc); err != ErrServerShutdown {
+		t.Fatal(err)
+	}
+
+	server.Shutdown(context.Background())
+	if clientErr != nil {
+		t.Fatal(clientErr)
+	}
+}