diff --git a/abci/client/client.go b/abci/client/client.go
index c5c1ab219a..0bfe7d4970 100644
--- a/abci/client/client.go
+++ b/abci/client/client.go
@@ -81,7 +81,7 @@ type ReqRes struct {
 	*sync.WaitGroup
 	*types.Response // Not set atomically, so be sure to use WaitGroup.
 
-	mtx  tmsync.Mutex
+	mtx  tmsync.RWMutex
 	done bool                  // Gets set to true once *after* WaitGroup.Done().
 	cb   func(*types.Response) // A single callback that may be set.
 }
@@ -131,16 +131,16 @@ func (r *ReqRes) InvokeCallback() {
 //
 // ref: https://github.com/tendermint/tendermint/issues/5439
 func (r *ReqRes) GetCallback() func(*types.Response) {
-	r.mtx.Lock()
-	defer r.mtx.Unlock()
+	r.mtx.RLock()
+	defer r.mtx.RUnlock()
 	return r.cb
 }
 
 // SetDone marks the ReqRes object as done.
 func (r *ReqRes) SetDone() {
 	r.mtx.Lock()
+	defer r.mtx.Unlock()
 	r.done = true
-	r.mtx.Unlock()
 }
 
 func waitGroup1() (wg *sync.WaitGroup) {
diff --git a/abci/client/grpc_client.go b/abci/client/grpc_client.go
index b375c6cc9c..71f460d2bd 100644
--- a/abci/client/grpc_client.go
+++ b/abci/client/grpc_client.go
@@ -27,7 +27,7 @@ type grpcClient struct {
 	conn     *grpc.ClientConn
 	chReqRes chan *ReqRes // dispatches "async" responses to callbacks *in order*, needed by mempool
 
-	mtx   tmsync.Mutex
+	mtx   tmsync.RWMutex
 	addr  string
 	err   error
 	resCb func(*types.Request, *types.Response) // listens to all callbacks
@@ -146,8 +146,8 @@ func (cli *grpcClient) StopForError(err error) {
 }
 
 func (cli *grpcClient) Error() error {
-	cli.mtx.Lock()
-	defer cli.mtx.Unlock()
+	cli.mtx.RLock()
+	defer cli.mtx.RUnlock()
 	return cli.err
 }
 
@@ -155,8 +155,8 @@ func (cli *grpcClient) Error() error {
 // NOTE: callback may get internally generated flush responses.
 func (cli *grpcClient) SetResponseCallback(resCb Callback) {
 	cli.mtx.Lock()
+	defer cli.mtx.Unlock()
 	cli.resCb = resCb
-	cli.mtx.Unlock()
 }
 
 //----------------------------------------
diff --git a/abci/client/local_client.go b/abci/client/local_client.go
index b3bdc451dc..09e6446410 100644
--- a/abci/client/local_client.go
+++ b/abci/client/local_client.go
@@ -15,27 +15,35 @@ var _ Client = (*localClient)(nil)
 type localClient struct {
 	service.BaseService
 
-	mtx *tmsync.Mutex
+	mtx *tmsync.RWMutex
 	types.Application
 	Callback
 }
 
-func NewLocalClient(mtx *tmsync.Mutex, app types.Application) Client {
+var _ Client = (*localClient)(nil)
+
+// NewLocalClient creates a local client, which will be directly calling the
+// methods of the given app.
+//
+// Both Async and Sync methods ignore the given context.Context parameter.
+func NewLocalClient(mtx *tmsync.RWMutex, app types.Application) Client {
 	if mtx == nil {
-		mtx = new(tmsync.Mutex)
+		mtx = &tmsync.RWMutex{}
 	}
+
 	cli := &localClient{
 		mtx:         mtx,
 		Application: app,
 	}
+
 	cli.BaseService = *service.NewBaseService(nil, "localClient", cli)
 	return cli
 }
 
 func (app *localClient) SetResponseCallback(cb Callback) {
 	app.mtx.Lock()
+	defer app.mtx.Unlock()
 	app.Callback = cb
-	app.mtx.Unlock()
 }
 
 // TODO: change types.Application to include Error()?
@@ -59,8 +67,8 @@ func (app *localClient) EchoAsync(msg string) *ReqRes {
 }
 
 func (app *localClient) InfoAsync(req types.RequestInfo) *ReqRes {
-	app.mtx.Lock()
-	defer app.mtx.Unlock()
+	app.mtx.RLock()
+	defer app.mtx.RUnlock()
 
 	res := app.Application.Info(req)
 	return app.callback(
@@ -103,8 +111,8 @@ func (app *localClient) CheckTxAsync(req types.RequestCheckTx) *ReqRes {
 }
 
 func (app *localClient) QueryAsync(req types.RequestQuery) *ReqRes {
-	app.mtx.Lock()
-	defer app.mtx.Unlock()
+	app.mtx.RLock()
+	defer app.mtx.RUnlock()
 
 	res := app.Application.Query(req)
 	return app.callback(
@@ -212,8 +220,8 @@ func (app *localClient) EchoSync(msg string) (*types.ResponseEcho, error) {
 }
 
 func (app *localClient) InfoSync(req types.RequestInfo) (*types.ResponseInfo, error) {
-	app.mtx.Lock()
-	defer app.mtx.Unlock()
+	app.mtx.RLock()
+	defer app.mtx.RUnlock()
 
 	res := app.Application.Info(req)
 	return &res, nil
@@ -244,8 +252,8 @@ func (app *localClient) CheckTxSync(req types.RequestCheckTx) (*types.ResponseCh
 }
 
 func (app *localClient) QuerySync(req types.RequestQuery) (*types.ResponseQuery, error) {
-	app.mtx.Lock()
-	defer app.mtx.Unlock()
+	app.mtx.RLock()
+	defer app.mtx.RUnlock()
 
 	res := app.Application.Query(req)
 	return &res, nil
diff --git a/abci/client/socket_client.go b/abci/client/socket_client.go
index a369f878c7..fd32315a60 100644
--- a/abci/client/socket_client.go
+++ b/abci/client/socket_client.go
@@ -34,7 +34,7 @@ type socketClient struct {
 	reqQueue   chan *ReqRes
 	flushTimer *timer.ThrottleTimer
 
-	mtx     tmsync.Mutex
+	mtx     tmsync.RWMutex
 	err     error
 	reqSent *list.List                            // list of requests sent, waiting for response
 	resCb   func(*types.Request, *types.Response) // called on all requests, if set.
@@ -99,8 +99,8 @@ func (cli *socketClient) OnStop() {
 
 // Error returns an error if the client was stopped abruptly.
 func (cli *socketClient) Error() error {
-	cli.mtx.Lock()
-	defer cli.mtx.Unlock()
+	cli.mtx.RLock()
+	defer cli.mtx.RUnlock()
 	return cli.err
 }
 
@@ -110,8 +110,8 @@ func (cli *socketClient) Error() error {
 // NOTE: callback may get internally generated flush responses.
 func (cli *socketClient) SetResponseCallback(resCb Callback) {
 	cli.mtx.Lock()
+	defer cli.mtx.Unlock()
 	cli.resCb = resCb
-	cli.mtx.Unlock()
 }
 
 //----------------------------------------
diff --git a/consensus/byzantine_test.go b/consensus/byzantine_test.go
index f5e372ae22..7df7004162 100644
--- a/consensus/byzantine_test.go
+++ b/consensus/byzantine_test.go
@@ -59,7 +59,7 @@ func TestByzantinePrevoteEquivocation(t *testing.T) {
 		blockStore := store.NewBlockStore(blockDB)
 
 		// one for mempool, one for consensus
-		mtx := new(tmsync.Mutex)
+		mtx := new(tmsync.RWMutex)
 		proxyAppConnMem := abcicli.NewLocalClient(mtx, app)
 		proxyAppConnCon := abcicli.NewLocalClient(mtx, app)
 
diff --git a/consensus/common_test.go b/consensus/common_test.go
index 60bb9eed5c..62bc89633e 100644
--- a/consensus/common_test.go
+++ b/consensus/common_test.go
@@ -389,7 +389,7 @@ func newStateWithConfigAndBlockStore(
 	blockStore := store.NewBlockStore(blockDB)
 
 	// one for mempool, one for consensus
-	mtx := new(tmsync.Mutex)
+	mtx := new(tmsync.RWMutex)
 	proxyAppConnMem := abcicli.NewLocalClient(mtx, app)
 	proxyAppConnCon := abcicli.NewLocalClient(mtx, app)
 
diff --git a/consensus/reactor_test.go b/consensus/reactor_test.go
index f23ec727dc..39a730d13d 100644
--- a/consensus/reactor_test.go
+++ b/consensus/reactor_test.go
@@ -153,7 +153,7 @@ func TestReactorWithEvidence(t *testing.T) {
 		blockStore := store.NewBlockStore(blockDB)
 
 		// one for mempool, one for consensus
-		mtx := new(tmsync.Mutex)
+		mtx := new(tmsync.RWMutex)
 		proxyAppConnMem := abcicli.NewLocalClient(mtx, app)
 		proxyAppConnCon := abcicli.NewLocalClient(mtx, app)
 
diff --git a/proxy/client.go b/proxy/client.go
index 1dc6d8853f..27baa9738a 100644
--- a/proxy/client.go
+++ b/proxy/client.go
@@ -20,7 +20,7 @@ type ClientCreator interface {
 // local proxy uses a mutex on an in-proc app
 
 type localClientCreator struct {
-	mtx *tmsync.Mutex
+	mtx *tmsync.RWMutex
 	app types.Application
 }
 
@@ -28,7 +28,7 @@ type localClientCreator struct {
 // which will be running locally.
 func NewLocalClientCreator(app types.Application) ClientCreator {
 	return &localClientCreator{
-		mtx: new(tmsync.Mutex),
+		mtx: new(tmsync.RWMutex),
 		app: app,
 	}
 }