diff --git a/eth/protocols/eth/peer.go b/eth/protocols/eth/peer.go
index 98273ccfc..1b4cfeb3d 100644
--- a/eth/protocols/eth/peer.go
+++ b/eth/protocols/eth/peer.go
@@ -75,12 +75,12 @@ type Peer struct {
 	head common.Hash // Latest advertised head block hash
 	td   *big.Int    // Latest advertised head block total difficulty
 
-	knownBlocks     mapset.Set             // Set of block hashes known to be known by this peer
+	knownBlocks     *knownCache            // Set of block hashes known to be known by this peer
 	queuedBlocks    chan *blockPropagation // Queue of blocks to broadcast to the peer
 	queuedBlockAnns chan *types.Block      // Queue of blocks to announce to the peer
 
 	txpool      TxPool             // Transaction pool used by the broadcasters for liveness checks
-	knownTxs    mapset.Set         // Set of transaction hashes known to be known by this peer
+	knownTxs    *knownCache        // Set of transaction hashes known to be known by this peer
 	txBroadcast chan []common.Hash // Channel used to queue transaction propagation requests
 	txAnnounce  chan []common.Hash // Channel used to queue transaction announcement requests
 
@@ -96,8 +96,8 @@ func NewPeer(version uint, p *p2p.Peer, rw p2p.MsgReadWriter, txpool TxPool) *Pe
 		Peer:            p,
 		rw:              rw,
 		version:         version,
-		knownTxs:        mapset.NewSet(),
-		knownBlocks:     mapset.NewSet(),
+		knownTxs:        newKnownCache(maxKnownTxs),
+		knownBlocks:     newKnownCache(maxKnownBlocks),
 		queuedBlocks:    make(chan *blockPropagation, maxQueuedBlocks),
 		queuedBlockAnns: make(chan *types.Block, maxQueuedBlockAnns),
 		txBroadcast:     make(chan []common.Hash),
@@ -162,9 +162,6 @@ func (p *Peer) KnownTransaction(hash common.Hash) bool {
 // never be propagated to this particular peer.
 func (p *Peer) markBlock(hash common.Hash) {
 	// If we reached the memory allowance, drop a previously known block hash
-	for p.knownBlocks.Cardinality() >= maxKnownBlocks {
-		p.knownBlocks.Pop()
-	}
 	p.knownBlocks.Add(hash)
 }
 
@@ -172,9 +169,6 @@ func (p *Peer) markBlock(hash common.Hash) {
 // will never be propagated to this particular peer.
 func (p *Peer) markTransaction(hash common.Hash) {
 	// If we reached the memory allowance, drop a previously known transaction hash
-	for p.knownTxs.Cardinality() >= maxKnownTxs {
-		p.knownTxs.Pop()
-	}
 	p.knownTxs.Add(hash)
 }
 
@@ -189,9 +183,6 @@ func (p *Peer) markTransaction(hash common.Hash) {
 // tests that directly send messages without having to do the asyn queueing.
 func (p *Peer) SendTransactions(txs types.Transactions) error {
 	// Mark all the transactions as known, but ensure we don't overflow our limits
-	for p.knownTxs.Cardinality() > max(0, maxKnownTxs-len(txs)) {
-		p.knownTxs.Pop()
-	}
 	for _, tx := range txs {
 		p.knownTxs.Add(tx.Hash())
 	}
@@ -205,12 +196,7 @@ func (p *Peer) AsyncSendTransactions(hashes []common.Hash) {
 	select {
 	case p.txBroadcast <- hashes:
 		// Mark all the transactions as known, but ensure we don't overflow our limits
-		for p.knownTxs.Cardinality() > max(0, maxKnownTxs-len(hashes)) {
-			p.knownTxs.Pop()
-		}
-		for _, hash := range hashes {
-			p.knownTxs.Add(hash)
-		}
+		p.knownTxs.Add(hashes...)
 	case <-p.term:
 		p.Log().Debug("Dropping transaction propagation", "count", len(hashes))
 	}
@@ -224,12 +210,7 @@ func (p *Peer) AsyncSendTransactions(hashes []common.Hash) {
 // not be managed directly.
 func (p *Peer) sendPooledTransactionHashes(hashes []common.Hash) error {
 	// Mark all the transactions as known, but ensure we don't overflow our limits
-	for p.knownTxs.Cardinality() > max(0, maxKnownTxs-len(hashes)) {
-		p.knownTxs.Pop()
-	}
-	for _, hash := range hashes {
-		p.knownTxs.Add(hash)
-	}
+	p.knownTxs.Add(hashes...)
 	return p2p.Send(p.rw, NewPooledTransactionHashesMsg, NewPooledTransactionHashesPacket(hashes))
 }
 
@@ -240,12 +221,7 @@ func (p *Peer) AsyncSendPooledTransactionHashes(hashes []common.Hash) {
 	select {
 	case p.txAnnounce <- hashes:
 		// Mark all the transactions as known, but ensure we don't overflow our limits
-		for p.knownTxs.Cardinality() > max(0, maxKnownTxs-len(hashes)) {
-			p.knownTxs.Pop()
-		}
-		for _, hash := range hashes {
-			p.knownTxs.Add(hash)
-		}
+		p.knownTxs.Add(hashes...)
 	case <-p.term:
 		p.Log().Debug("Dropping transaction announcement", "count", len(hashes))
 	}
@@ -254,12 +230,8 @@ func (p *Peer) AsyncSendPooledTransactionHashes(hashes []common.Hash) {
 // ReplyPooledTransactionsRLP is the eth/66 version of SendPooledTransactionsRLP.
 func (p *Peer) ReplyPooledTransactionsRLP(id uint64, hashes []common.Hash, txs []rlp.RawValue) error {
 	// Mark all the transactions as known, but ensure we don't overflow our limits
-	for p.knownTxs.Cardinality() > max(0, maxKnownTxs-len(hashes)) {
-		p.knownTxs.Pop()
-	}
-	for _, hash := range hashes {
-		p.knownTxs.Add(hash)
-	}
+	p.knownTxs.Add(hashes...)
+
 	// Not packed into PooledTransactionsPacket to avoid RLP decoding
 	return p2p.Send(p.rw, PooledTransactionsMsg, PooledTransactionsRLPPacket66{
 		RequestId:                   id,
@@ -271,12 +243,8 @@ func (p *Peer) ReplyPooledTransactionsRLP(id uint64, hashes []common.Hash, txs [
 // a hash notification.
 func (p *Peer) SendNewBlockHashes(hashes []common.Hash, numbers []uint64) error {
 	// Mark all the block hashes as known, but ensure we don't overflow our limits
-	for p.knownBlocks.Cardinality() > max(0, maxKnownBlocks-len(hashes)) {
-		p.knownBlocks.Pop()
-	}
-	for _, hash := range hashes {
-		p.knownBlocks.Add(hash)
-	}
+	p.knownBlocks.Add(hashes...)
+
 	request := make(NewBlockHashesPacket, len(hashes))
 	for i := 0; i < len(hashes); i++ {
 		request[i].Hash = hashes[i]
@@ -292,9 +260,6 @@ func (p *Peer) AsyncSendNewBlockHash(block *types.Block) {
 	select {
 	case p.queuedBlockAnns <- block:
 		// Mark all the block hash as known, but ensure we don't overflow our limits
-		for p.knownBlocks.Cardinality() >= maxKnownBlocks {
-			p.knownBlocks.Pop()
-		}
 		p.knownBlocks.Add(block.Hash())
 	default:
 		p.Log().Debug("Dropping block announcement", "number", block.NumberU64(), "hash", block.Hash())
@@ -304,9 +269,6 @@ func (p *Peer) AsyncSendNewBlockHash(block *types.Block) {
 // SendNewBlock propagates an entire block to a remote peer.
 func (p *Peer) SendNewBlock(block *types.Block, td *big.Int) error {
 	// Mark all the block hash as known, but ensure we don't overflow our limits
-	for p.knownBlocks.Cardinality() >= maxKnownBlocks {
-		p.knownBlocks.Pop()
-	}
 	p.knownBlocks.Add(block.Hash())
 	return p2p.Send(p.rw, NewBlockMsg, &NewBlockPacket{
 		Block: block,
@@ -320,9 +282,6 @@ func (p *Peer) AsyncSendNewBlock(block *types.Block, td *big.Int) {
 	select {
 	case p.queuedBlocks <- &blockPropagation{block: block, td: td}:
 		// Mark all the block hash as known, but ensure we don't overflow our limits
-		for p.knownBlocks.Cardinality() >= maxKnownBlocks {
-			p.knownBlocks.Pop()
-		}
 		p.knownBlocks.Add(block.Hash())
 	default:
 		p.Log().Debug("Dropping block propagation", "number", block.NumberU64(), "hash", block.Hash())
@@ -465,3 +424,37 @@ func (p *Peer) RequestTxs(hashes []common.Hash) error {
 		GetPooledTransactionsPacket: hashes,
 	})
 }
+
+// knownCache is a cache for known hashes.
+type knownCache struct {
+	hashes mapset.Set
+	max    int
+}
+
+// newKnownCache creates a new knownCache with a max capacity.
+func newKnownCache(max int) *knownCache {
+	return &knownCache{
+		max:    max,
+		hashes: mapset.NewSet(),
+	}
+}
+
+// Add adds a list of elements to the set.
+func (k *knownCache) Add(hashes ...common.Hash) {
+	for k.hashes.Cardinality() > max(0, k.max-len(hashes)) {
+		k.hashes.Pop()
+	}
+	for _, hash := range hashes {
+		k.hashes.Add(hash)
+	}
+}
+
+// Contains returns whether the given item is in the set.
+func (k *knownCache) Contains(hash common.Hash) bool {
+	return k.hashes.Contains(hash)
+}
+
+// Cardinality returns the number of elements in the set.
+func (k *knownCache) Cardinality() int {
+	return k.hashes.Cardinality()
+}
diff --git a/eth/protocols/eth/peer_test.go b/eth/protocols/eth/peer_test.go
index 70e9959f8..fc9344370 100644
--- a/eth/protocols/eth/peer_test.go
+++ b/eth/protocols/eth/peer_test.go
@@ -21,7 +21,9 @@ package eth
 
 import (
 	"crypto/rand"
+	"testing"
 
+	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/p2p"
 	"github.com/ethereum/go-ethereum/p2p/enode"
 )
@@ -59,3 +61,28 @@ func (p *testPeer) close() {
 	p.Peer.Close()
 	p.app.Close()
 }
+
+func TestPeerSet(t *testing.T) {
+	size := 5
+	s := newKnownCache(size)
+
+	// add 10 items
+	for i := 0; i < size*2; i++ {
+		s.Add(common.Hash{byte(i)})
+	}
+
+	if s.Cardinality() != size {
+		t.Fatalf("wrong size, expected %d but found %d", size, s.Cardinality())
+	}
+
+	vals := []common.Hash{}
+	for i := 10; i < 20; i++ {
+		vals = append(vals, common.Hash{byte(i)})
+	}
+
+	// add item in batch
+	s.Add(vals...)
+	if s.Cardinality() < size {
+		t.Fatalf("bad size")
+	}
+}