diff --git a/ackhandlernew/received_packet_history.go b/ackhandlernew/received_packet_history.go
index e843668a4..608703da6 100644
--- a/ackhandlernew/received_packet_history.go
+++ b/ackhandlernew/received_packet_history.go
@@ -61,6 +61,22 @@ func (h *receivedPacketHistory) ReceivedPacket(p protocol.PacketNumber) {
 	h.ranges.InsertBefore(utils.PacketInterval{Start: p, End: p}, h.ranges.Front())
 }
 
+func (h *receivedPacketHistory) DeleteBelow(leastUnacked protocol.PacketNumber) {
+	nextEl := h.ranges.Front()
+	for el := h.ranges.Front(); nextEl != nil; el = nextEl {
+		nextEl = el.Next()
+
+		if leastUnacked > el.Value.Start && leastUnacked <= el.Value.End {
+			el.Value.Start = leastUnacked
+		}
+		if el.Value.End < leastUnacked { // delete a whole range
+			h.ranges.Remove(el)
+		} else {
+			return
+		}
+	}
+}
+
 // GetAckRanges gets a slice of all AckRanges that can be used in an AckFrame
 func (h *receivedPacketHistory) GetAckRanges() []frames.AckRange {
 	if h.ranges.Len() == 0 {
diff --git a/ackhandlernew/received_packet_history_test.go b/ackhandlernew/received_packet_history_test.go
index 5088e83dd..7f8f0ca07 100644
--- a/ackhandlernew/received_packet_history_test.go
+++ b/ackhandlernew/received_packet_history_test.go
@@ -121,6 +121,58 @@ var _ = Describe("receivedPacketHistory", func() {
 		})
 	})
 
+	Context("deleting", func() {
+		It("does nothing when the history is empty", func() {
+			hist.DeleteBelow(5)
+			Expect(hist.ranges.Len()).To(BeZero())
+		})
+
+		It("deletes a range", func() {
+			hist.ReceivedPacket(4)
+			hist.ReceivedPacket(5)
+			hist.ReceivedPacket(10)
+			hist.DeleteBelow(6)
+			Expect(hist.ranges.Len()).To(Equal(1))
+			Expect(hist.ranges.Front().Value).To(Equal(utils.PacketInterval{Start: 10, End: 10}))
+		})
+
+		It("deletes multiple ranges", func() {
+			hist.ReceivedPacket(1)
+			hist.ReceivedPacket(5)
+			hist.ReceivedPacket(10)
+			hist.DeleteBelow(8)
+			Expect(hist.ranges.Len()).To(Equal(1))
+			Expect(hist.ranges.Front().Value).To(Equal(utils.PacketInterval{Start: 10, End: 10}))
+		})
+
+		It("adjusts a range, if leastUnacked lies inside it", func() {
+			hist.ReceivedPacket(3)
+			hist.ReceivedPacket(4)
+			hist.ReceivedPacket(5)
+			hist.ReceivedPacket(6)
+			hist.DeleteBelow(4)
+			Expect(hist.ranges.Len()).To(Equal(1))
+			Expect(hist.ranges.Front().Value).To(Equal(utils.PacketInterval{Start: 4, End: 6}))
+		})
+
+		It("adjusts a range, if leastUnacked is the last of the range", func() {
+			hist.ReceivedPacket(4)
+			hist.ReceivedPacket(5)
+			hist.ReceivedPacket(10)
+			hist.DeleteBelow(5)
+			Expect(hist.ranges.Len()).To(Equal(2))
+			Expect(hist.ranges.Front().Value).To(Equal(utils.PacketInterval{Start: 5, End: 5}))
+			Expect(hist.ranges.Back().Value).To(Equal(utils.PacketInterval{Start: 10, End: 10}))
+		})
+
+		It("keeps a one-packet range, if leastUnacked is exactly that value", func() {
+			hist.ReceivedPacket(4)
+			hist.DeleteBelow(4)
+			Expect(hist.ranges.Len()).To(Equal(1))
+			Expect(hist.ranges.Front().Value).To(Equal(utils.PacketInterval{Start: 4, End: 4}))
+		})
+	})
+
 	Context("ACK range export", func() {
 		It("returns nil if there are no ranges", func() {
 			Expect(hist.GetAckRanges()).To(BeNil())