diff --git a/13.go b/13.go
index f65237d..2eeb39e 100644
--- a/13.go
+++ b/13.go
@@ -15,6 +15,7 @@ import (
 	"io"
 	"os"
 	"runtime/debug"
+	"sync/atomic"
 	"time"
 
 	"golang_org/x/crypto/curve25519"
@@ -157,6 +158,7 @@ func (hs *serverHandshakeState) readClientFinished13() error {
 
 	c.hs = nil // Discard the server handshake state
 	c.phase = handshakeConfirmed
+	atomic.StoreInt32(&c.handshakeConfirmed, 1)
 	c.in.setCipher(c.vers, hs.appClientCipher)
 	c.in.traceErr, c.out.traceErr = nil, nil
 
diff --git a/conn.go b/conn.go
index 27acbef..ac78161 100644
--- a/conn.go
+++ b/conn.go
@@ -27,21 +27,25 @@ type Conn struct {
 	conn     net.Conn
 	isClient bool
 
+	phase handshakeStatus // protected by in.Mutex
+	// handshakeConfirmed is an atomic bool for phase == handshakeConfirmed
+	handshakeConfirmed int32
+
 	// constant after handshake; protected by handshakeMutex
 	handshakeMutex sync.Mutex // handshakeMutex < in.Mutex, out.Mutex, errMutex
 	// handshakeCond, if not nil, indicates that a goroutine is committed
 	// to running the handshake for this Conn. Other goroutines that need
 	// to wait for the handshake can wait on this, under handshakeMutex.
 	handshakeCond *sync.Cond
-	// The transition from handshakeRunning to the next phase is covered by
-	// handshakeMutex. All others by in.Mutex.
-	phase        handshakeStatus
-	handshakeErr error   // error resulting from handshake
-	connID       []byte  // Random connection id
-	clientHello  []byte  // ClientHello packet contents
-	vers         uint16  // TLS version
-	haveVers     bool    // version has been negotiated
-	config       *Config // configuration passed to constructor
+	handshakeErr  error   // error resulting from handshake
+	connID        []byte  // Random connection id
+	clientHello   []byte  // ClientHello packet contents
+	vers          uint16  // TLS version
+	haveVers      bool    // version has been negotiated
+	config        *Config // configuration passed to constructor
+	// handshakeComplete is true if the connection reached application data
+	// and it's equivalent to phase > handshakeRunning
+	handshakeComplete bool
 	// handshakes counts the number of handshakes performed on the
 	// connection so far. If renegotiation is disabled then this is either
 	// zero or one.
@@ -1160,7 +1164,7 @@ func (c *Conn) Write(b []byte) (int, error) {
 		return 0, err
 	}
 
-	if c.phase == handshakeRunning {
+	if !c.handshakeComplete {
 		return 0, alertInternalError
 	}
 
@@ -1232,6 +1236,7 @@ func (c *Conn) handleRenegotiation() error {
 	defer c.handshakeMutex.Unlock()
 
 	c.phase = handshakeRunning
+	c.handshakeComplete = false
 	if c.handshakeErr = c.clientHandshake(); c.handshakeErr == nil {
 		c.handshakes++
 	}
@@ -1289,12 +1294,13 @@ func (c *Conn) ConfirmHandshake() error {
 	return nil
 }
 
-// earlyDataReader wraps a Conn with in locked and reads only early data,
-// both buffered and still on the wire.
+// earlyDataReader wraps a Conn and reads only early data, both buffered
+// and still on the wire.
 type earlyDataReader struct {
 	c *Conn
 }
 
+// c.in.Mutex <= L
 func (r earlyDataReader) Read(b []byte) (n int, err error) {
 	c := r.c
 
@@ -1423,7 +1429,7 @@ func (c *Conn) Close() error {
 	var alertErr error
 
 	c.handshakeMutex.Lock()
-	if c.phase != handshakeRunning {
+	if c.handshakeComplete {
 		alertErr = c.closeNotify()
 	}
 	c.handshakeMutex.Unlock()
@@ -1442,7 +1448,7 @@ var errEarlyCloseWrite = errors.New("tls: CloseWrite called before handshake com
 func (c *Conn) CloseWrite() error {
 	c.handshakeMutex.Lock()
 	defer c.handshakeMutex.Unlock()
-	if c.phase == handshakeRunning {
+	if !c.handshakeComplete {
 		return errEarlyCloseWrite
 	}
 
@@ -1497,7 +1503,7 @@ func (c *Conn) Handshake() error {
 		if err := c.handshakeErr; err != nil {
 			return err
 		}
-		if c.phase != handshakeRunning {
+		if c.handshakeComplete {
 			return nil
 		}
 		if c.handshakeCond == nil {
@@ -1519,7 +1525,7 @@ func (c *Conn) Handshake() error {
 
 	// The handshake cannot have completed when handshakeMutex was unlocked
 	// because this goroutine set handshakeCond.
-	if c.handshakeErr != nil || c.phase != handshakeRunning {
+	if c.handshakeErr != nil || c.handshakeComplete {
 		panic("handshake should not have been able to complete after handshakeCond was set")
 	}
 
@@ -1541,7 +1547,7 @@ func (c *Conn) Handshake() error {
 		c.flush()
 	}
 
-	if c.handshakeErr == nil && c.phase == handshakeRunning {
+	if c.handshakeErr == nil && !c.handshakeComplete {
 		panic("handshake should have had a result.")
 	}
 
@@ -1559,10 +1565,10 @@ func (c *Conn) ConnectionState() ConnectionState {
 	defer c.handshakeMutex.Unlock()
 
 	var state ConnectionState
-	state.HandshakeComplete = c.phase != handshakeRunning
+	state.HandshakeComplete = c.handshakeComplete
 	state.ServerName = c.serverName
 
-	if state.HandshakeComplete {
+	if c.handshakeComplete {
 		state.ConnectionID = c.connID
 		state.ClientHello = c.clientHello
 		state.Version = c.vers
@@ -1574,7 +1580,7 @@ func (c *Conn) ConnectionState() ConnectionState {
 		state.VerifiedChains = c.verifiedChains
 		state.SignedCertificateTimestamps = c.scts
 		state.OCSPResponse = c.ocspResponse
-		state.HandshakeConfirmed = c.phase == handshakeConfirmed
+		state.HandshakeConfirmed = atomic.LoadInt32(&c.handshakeConfirmed) == 1
 		if !c.didResume {
 			if c.clientFinishedIsFirst {
 				state.TLSUnique = c.clientFinished[:]
@@ -1605,7 +1611,7 @@ func (c *Conn) VerifyHostname(host string) error {
 	if !c.isClient {
 		return errors.New("tls: VerifyHostname called on TLS server connection")
 	}
-	if c.phase == handshakeRunning {
+	if !c.handshakeComplete {
 		return errors.New("tls: handshake has not yet been performed")
 	}
 	if len(c.verifiedChains) == 0 {
diff --git a/handshake_client.go b/handshake_client.go
index 4ead1eb..a570649 100644
--- a/handshake_client.go
+++ b/handshake_client.go
@@ -17,6 +17,7 @@ import (
 	"net"
 	"strconv"
 	"strings"
+	"sync/atomic"
 )
 
 type clientHandshakeState struct {
@@ -252,6 +253,8 @@ NextCipherSuite:
 
 	c.didResume = isResume
 	c.phase = handshakeConfirmed
+	atomic.StoreInt32(&c.handshakeConfirmed, 1)
+	c.handshakeComplete = true
 	c.cipherSuite = suite.id
 	return nil
 }
diff --git a/handshake_server.go b/handshake_server.go
index 32630d8..652e8a1 100644
--- a/handshake_server.go
+++ b/handshake_server.go
@@ -15,6 +15,7 @@ import (
 	"fmt"
 	"hash"
 	"io"
+	"sync/atomic"
 )
 
 type Committer interface {
@@ -78,6 +79,8 @@ func (c *Conn) serverHandshake() error {
 			return err
 		}
 		c.hs = &hs
+		c.handshakeComplete = true
+		return nil
 	} else if isResume {
 		// The client has included a session ticket and so we do an abbreviated handshake.
 		if err := hs.doResumeHandshake(); err != nil {
@@ -105,7 +108,6 @@ func (c *Conn) serverHandshake() error {
 			return err
 		}
 		c.didResume = true
-		c.phase = handshakeConfirmed
 	} else {
 		// The client didn't include a session ticket, or it wasn't
 		// valid so we do a full handshake.
@@ -129,8 +131,10 @@ func (c *Conn) serverHandshake() error {
 		if _, err := c.flush(); err != nil {
 			return err
 		}
-		c.phase = handshakeConfirmed
 	}
+	c.phase = handshakeConfirmed
+	atomic.StoreInt32(&c.handshakeConfirmed, 1)
+	c.handshakeComplete = true
 
 	return nil
 }