diff --git a/ackhandler/received_packet_handler.go b/ackhandler/received_packet_handler.go
index 2aeecb86..e20fc416 100644
--- a/ackhandler/received_packet_handler.go
+++ b/ackhandler/received_packet_handler.go
@@ -53,7 +53,8 @@ func (h *receivedPacketHandler) ReceivedStopWaiting(f *frames.StopWaitingFrame)
 		return nil
 	}
 
-	h.highestInOrderObserved = f.LeastUnacked
+	// the LeastUnacked is the smallest packet number of any packet for which the sender is still awaiting an ack. So the highestInOrderObserved is one less than that
+	h.highestInOrderObserved = f.LeastUnacked - 1
 	h.highestInOrderObservedEntropy = EntropyAccumulator(f.Entropy)
 
 	return nil
diff --git a/ackhandler/received_packet_handler_test.go b/ackhandler/received_packet_handler_test.go
index 06815529..f218ddad 100644
--- a/ackhandler/received_packet_handler_test.go
+++ b/ackhandler/received_packet_handler_test.go
@@ -214,16 +214,16 @@ var _ = Describe("receivedPacketHandler", func() {
 			Expect(err).ToNot(HaveOccurred())
 			_, e := handler.getNackRanges()
 			Expect(e).To(Equal(42 ^ expectedAfterStopWaiting))
-			Expect(handler.highestInOrderObserved).To(Equal(protocol.PacketNumber(12)))
+			Expect(handler.highestInOrderObserved).To(Equal(protocol.PacketNumber(11)))
 			Expect(handler.highestInOrderObservedEntropy).To(Equal(EntropyAccumulator(42)))
 		})
 
-		It("does not emit nack ranges after STOP_WAITING", func() {
+		It("does not emit NACK ranges after STOP_WAITING", func() {
 			err := handler.ReceivedPacket(10, false)
 			Expect(err).ToNot(HaveOccurred())
 			ranges, _ := handler.getNackRanges()
 			Expect(ranges).To(HaveLen(1))
-			err = handler.ReceivedStopWaiting(&frames.StopWaitingFrame{Entropy: 0, LeastUnacked: protocol.PacketNumber(9)})
+			err = handler.ReceivedStopWaiting(&frames.StopWaitingFrame{Entropy: 0, LeastUnacked: protocol.PacketNumber(10)})
 			Expect(err).ToNot(HaveOccurred())
 			ranges, _ = handler.getNackRanges()
 			Expect(ranges).To(HaveLen(0))