diff --git a/consensus/mempool_test.go b/consensus/mempool_test.go
index 2a063be75..b2246ce54 100644
--- a/consensus/mempool_test.go
+++ b/consensus/mempool_test.go
@@ -2,7 +2,6 @@ package consensus
 
 import (
 	"encoding/binary"
-	//	"math/rand"
 	"testing"
 	"time"
 
@@ -52,6 +51,67 @@ func TestTxConcurrentWithCommit(t *testing.T) {
 	}
 }
 
+func TestRmBadTx(t *testing.T) {
+	state, privVals := randGenesisState(1, false, 10)
+	app := NewCounterApplication()
+	cs := newConsensusState(state, privVals[0], app)
+
+	// increment the counter by 1
+	txBytes := make([]byte, 8)
+	binary.BigEndian.PutUint64(txBytes, uint64(0))
+	app.AppendTx(txBytes)
+	app.Commit()
+
+	ch := make(chan struct{})
+	cbCh := make(chan struct{})
+	go func() {
+		// Try to send the tx through the mempool.
+		// CheckTx should not err, but the app should return a bad tmsp code
+		// and the tx should get removed from the pool
+		err := cs.mempool.CheckTx(txBytes, func(r *tmsp.Response) {
+			if r.GetCheckTx().Code != tmsp.CodeType_BadNonce {
+				t.Fatalf("expected checktx to return bad nonce, got %v", r)
+			}
+			cbCh <- struct{}{}
+		})
+		if err != nil {
+			t.Fatal("Error after CheckTx: %v", err)
+		}
+
+		// check for the tx
+		for {
+			time.Sleep(time.Second)
+			select {
+			case <-ch:
+			default:
+				txs := cs.mempool.Reap(1)
+				if len(txs) == 0 {
+					ch <- struct{}{}
+				}
+
+			}
+		}
+	}()
+
+	// Wait until the tx returns
+	ticker := time.After(time.Second * 5)
+	select {
+	case <-cbCh:
+		// success
+	case <-ticker:
+		t.Fatalf("Timed out waiting for tx to return")
+	}
+
+	// Wait until the tx is removed
+	ticker = time.After(time.Second * 5)
+	select {
+	case <-ch:
+		// success
+	case <-ticker:
+		t.Fatalf("Timed out waiting for tx to be removed")
+	}
+}
+
 // CounterApplication that maintains a mempool state and resets it upon commit
 type CounterApplication struct {
 	txCount        int
@@ -84,11 +144,7 @@ func runTx(tx []byte, countPtr *int) tmsp.Result {
 	copy(tx8[len(tx8)-len(tx):], tx)
 	txValue := binary.BigEndian.Uint64(tx8)
 	if txValue != uint64(count) {
-		return tmsp.Result{
-			Code: tmsp.CodeType_BadNonce,
-			Data: nil,
-			Log:  Fmt("Invalid nonce. Expected %v, got %v", count, txValue),
-		}
+		return tmsp.ErrBadNonce.AppendLog(Fmt("Invalid nonce. Expected %v, got %v", count, txValue))
 	}
 	*countPtr += 1
 	return tmsp.OK
diff --git a/mempool/mempool.go b/mempool/mempool.go
index acc52ae6e..2b7be1ddb 100644
--- a/mempool/mempool.go
+++ b/mempool/mempool.go
@@ -59,8 +59,7 @@ type Mempool struct {
 
 	// Keep a cache of already-seen txs.
 	// This reduces the pressure on the proxyApp.
-	cacheMap  map[string]struct{}
-	cacheList *list.List // to remove oldest tx when cache gets too big
+	cache *txCache
 }
 
 func NewMempool(config cfg.Config, proxyAppConn proxy.AppConnMempool) *Mempool {
@@ -74,8 +73,7 @@ func NewMempool(config cfg.Config, proxyAppConn proxy.AppConnMempool) *Mempool {
 		recheckCursor: nil,
 		recheckEnd:    nil,
 
-		cacheMap:  make(map[string]struct{}, cacheSize),
-		cacheList: list.New(),
+		cache: newTxCache(cacheSize),
 	}
 	proxyAppConn.SetResponseCallback(mempool.resCb)
 	return mempool
@@ -100,8 +98,7 @@ func (mem *Mempool) Flush() {
 	mem.proxyMtx.Lock()
 	defer mem.proxyMtx.Unlock()
 
-	mem.cacheMap = make(map[string]struct{}, cacheSize)
-	mem.cacheList.Init()
+	mem.cache.Reset()
 
 	for e := mem.txs.Front(); e != nil; e = e.Next() {
 		mem.txs.Remove(e)
@@ -125,7 +122,7 @@ func (mem *Mempool) CheckTx(tx types.Tx, cb func(*tmsp.Response)) (err error) {
 	defer mem.proxyMtx.Unlock()
 
 	// CACHE
-	if _, exists := mem.cacheMap[string(tx)]; exists {
+	if mem.cache.Exists(tx) {
 		if cb != nil {
 			cb(&tmsp.Response{
 				Value: &tmsp.Response_CheckTx{
@@ -138,16 +135,7 @@ func (mem *Mempool) CheckTx(tx types.Tx, cb func(*tmsp.Response)) (err error) {
 		}
 		return nil
 	}
-	if mem.cacheList.Len() >= cacheSize {
-		popped := mem.cacheList.Front()
-		poppedTx := popped.Value.(types.Tx)
-		// NOTE: the tx may have already been removed from the map
-		// but deleting a non-existant element is fine
-		delete(mem.cacheMap, string(poppedTx))
-		mem.cacheList.Remove(popped)
-	}
-	mem.cacheMap[string(tx)] = struct{}{}
-	mem.cacheList.PushBack(tx)
+	mem.cache.Push(tx)
 	// END CACHE
 
 	// NOTE: proxyAppConn may error if tx buffer is full
@@ -162,13 +150,6 @@ func (mem *Mempool) CheckTx(tx types.Tx, cb func(*tmsp.Response)) (err error) {
 	return nil
 }
 
-func (mem *Mempool) removeTxFromCacheMap(tx []byte) {
-	mem.proxyMtx.Lock()
-	// NOTE tx not removed from cacheList
-	delete(mem.cacheMap, string(tx))
-	mem.proxyMtx.Unlock()
-}
-
 // TMSP callback function
 func (mem *Mempool) resCb(req *tmsp.Request, res *tmsp.Response) {
 	if mem.recheckCursor == nil {
@@ -194,9 +175,7 @@ func (mem *Mempool) resCbNormal(req *tmsp.Request, res *tmsp.Response) {
 			log.Info("Bad Transaction", "res", r)
 
 			// remove from cache (it might be good later)
-			// note this is an async callback,
-			// so we need to grab the lock in removeTxFromCacheMap
-			mem.removeTxFromCacheMap(req.GetCheckTx().Tx)
+			mem.cache.Remove(req.GetCheckTx().Tx)
 
 			// TODO: handle other retcodes
 		}
@@ -221,7 +200,7 @@ func (mem *Mempool) resCbRecheck(req *tmsp.Request, res *tmsp.Response) {
 			mem.recheckCursor.DetachPrev()
 
 			// remove from cache (it might be good later)
-			mem.removeTxFromCacheMap(req.GetCheckTx().Tx)
+			mem.cache.Remove(req.GetCheckTx().Tx)
 		}
 		if mem.recheckCursor == mem.recheckEnd {
 			mem.recheckCursor = nil
@@ -348,3 +327,62 @@ type mempoolTx struct {
 func (memTx *mempoolTx) Height() int {
 	return int(atomic.LoadInt64(&memTx.height))
 }
+
+//--------------------------------------------------------------------------------
+
+type txCache struct {
+	mtx  sync.Mutex
+	size int
+	map_ map[string]struct{}
+	list *list.List // to remove oldest tx when cache gets too big
+}
+
+func newTxCache(cacheSize int) *txCache {
+	return &txCache{
+		size: cacheSize,
+		map_: make(map[string]struct{}, cacheSize),
+		list: list.New(),
+	}
+}
+
+func (cache *txCache) Reset() {
+	cache.mtx.Lock()
+	cache.map_ = make(map[string]struct{}, cacheSize)
+	cache.list.Init()
+	cache.mtx.Unlock()
+}
+
+func (cache *txCache) Exists(tx types.Tx) bool {
+	cache.mtx.Lock()
+	_, exists := cache.map_[string(tx)]
+	cache.mtx.Unlock()
+	return exists
+}
+
+// Returns false if tx is in cache.
+func (cache *txCache) Push(tx types.Tx) bool {
+	cache.mtx.Lock()
+	defer cache.mtx.Unlock()
+
+	if _, exists := cache.map_[string(tx)]; exists {
+		return false
+	}
+
+	if cache.list.Len() >= cache.size {
+		popped := cache.list.Front()
+		poppedTx := popped.Value.(types.Tx)
+		// NOTE: the tx may have already been removed from the map
+		// but deleting a non-existant element is fine
+		delete(cache.map_, string(poppedTx))
+		cache.list.Remove(popped)
+	}
+	cache.map_[string(tx)] = struct{}{}
+	cache.list.PushBack(tx)
+	return true
+}
+
+func (cache *txCache) Remove(tx types.Tx) {
+	cache.mtx.Lock()
+	delete(cache.map_, string(tx))
+	cache.mtx.Unlock()
+}
diff --git a/mempool/mempool_test.go b/mempool/mempool_test.go
index d5bd6b130..4755bf096 100644
--- a/mempool/mempool_test.go
+++ b/mempool/mempool_test.go
@@ -2,12 +2,11 @@ package mempool
 
 import (
 	"encoding/binary"
-	"sync"
 	"testing"
 
 	"github.com/tendermint/tendermint/config/tendermint_test"
+	"github.com/tendermint/tendermint/proxy"
 	"github.com/tendermint/tendermint/types"
-	tmspcli "github.com/tendermint/tmsp/client"
 	"github.com/tendermint/tmsp/example/counter"
 )
 
@@ -16,9 +15,9 @@ func TestSerialReap(t *testing.T) {
 
 	app := counter.NewCounterApplication(true)
 	app.SetOption("serial", "on")
-	mtx := new(sync.Mutex)
-	appConnMem := tmspcli.NewLocalClient(mtx, app)
-	appConnCon := tmspcli.NewLocalClient(mtx, app)
+	cc := proxy.NewLocalClientCreator(app)
+	appConnMem, _ := cc.NewTMSPClient()
+	appConnCon, _ := cc.NewTMSPClient()
 	mempool := NewMempool(config, appConnMem)
 
 	appendTxsRange := func(start, end int) {
@@ -66,13 +65,13 @@ func TestSerialReap(t *testing.T) {
 		for i := start; i < end; i++ {
 			txBytes := make([]byte, 8)
 			binary.BigEndian.PutUint64(txBytes, uint64(i))
-			res := appConnCon.AppendTx(txBytes)
+			res := appConnCon.AppendTxSync(txBytes)
 			if !res.IsOK() {
 				t.Errorf("Error committing tx. Code:%v result:%X log:%v",
 					res.Code, res.Data, res.Log)
 			}
 		}
-		res := appConnCon.Commit()
+		res := appConnCon.CommitSync()
 		if len(res.Data) != 8 {
 			t.Errorf("Error committing. Hash:%X log:%v", res.Data, res.Log)
 		}