diff --git a/cool/conn.go b/cool/conn.go
index 511e79b..81f49e5 100644
--- a/cool/conn.go
+++ b/cool/conn.go
@@ -25,7 +25,7 @@ var _ net.Conn = (*Conn)(nil)
 
 type Conn struct {
 	net.Conn
-	sync.RWMutex
+	mu       sync.RWMutex
 	unusable bool
 	c        *cool
 	t        time.Time
@@ -34,8 +34,8 @@ type Conn struct {
 // Close overrides the net.Conn Close method
 // put the usable connection back to the pool instead of closing it
 func (cc *Conn) Close() error {
-	cc.RLock()
-	defer cc.RUnlock()
+	cc.mu.RLock()
+	defer cc.mu.RUnlock()
 	if cc.unusable {
 		if cc.Conn != nil {
 			return cc.Conn.Close()
@@ -46,13 +46,13 @@ func (cc *Conn) Close() error {
 }
 
 func (cc *Conn) MarkUnusable() {
-	cc.Lock()
-	defer cc.Unlock()
+	cc.mu.Lock()
+	defer cc.mu.Unlock()
 	cc.unusable = true
 }
 
 func (cc *Conn) IsUnusable() bool {
-	cc.RLock()
-	defer cc.RUnlock()
+	cc.mu.RLock()
+	defer cc.mu.RUnlock()
 	return cc.unusable
 }
diff --git a/cool/cool.go b/cool/cool.go
index 057dc40..e692428 100644
--- a/cool/cool.go
+++ b/cool/cool.go
@@ -41,8 +41,8 @@ type Cool interface {
 type Producer func() (net.Conn, error)
 
 type cool struct {
-	sync.Once
-	sync.RWMutex
+	once     sync.Once
+	mu       sync.RWMutex
 	options  *options
 	connC    chan net.Conn
 	producer Producer
@@ -69,10 +69,10 @@ func New(init, max int, producer Producer, opts ...Option) (Cool, error) {
 }
 
 func (c *cool) Get() (net.Conn, error) {
-	c.RLock()
+	c.mu.RLock()
 	connC := c.connC
 	producer := c.producer
-	c.RUnlock()
+	c.mu.RUnlock()
 	if connC == nil {
 		return nil, ErrClosed
 	}
@@ -91,7 +91,7 @@ func (c *cool) Get() (net.Conn, error) {
 }
 
 func (c *cool) Close() {
-	c.Do(func() {
+	c.once.Do(func() {
 		connC := c.connC
 		c.options = nil
 		c.connC = nil
@@ -104,8 +104,8 @@ func (c *cool) Close() {
 }
 
 func (c *cool) Len() int {
-	c.RLock()
-	defer c.RUnlock()
+	c.mu.RLock()
+	defer c.mu.RUnlock()
 	return len(c.connC)
 }
 
@@ -113,8 +113,8 @@ func (c *cool) put(conn net.Conn) error {
 	if conn == nil {
 		return ErrNilConn
 	}
-	c.RLock()
-	defer c.RUnlock()
+	c.mu.RLock()
+	defer c.mu.RUnlock()
 	if c.connC == nil {
 		// cool is closed
 		return conn.Close()