diff --git a/blacklist.go b/blacklist.go
index 024796d..9ecf662 100644
--- a/blacklist.go
+++ b/blacklist.go
@@ -22,7 +22,7 @@ type MemBlacklist struct {
 	list BlacklistMap
 }
 
-// NewMemBlacklist
+// NewMemBlacklist implements the Blacklist interface using an in-memory map
 func NewMemBlacklist() *MemBlacklist {
 	return &MemBlacklist{list: make(BlacklistMap)}
 }
diff --git a/jwt.go b/jwt.go
index 1268cb2..32a9012 100644
--- a/jwt.go
+++ b/jwt.go
@@ -11,6 +11,7 @@ import (
 	"errors"
 	"io"
 	"strings"
+	"sync"
 	"time"
 )
 
@@ -50,6 +51,7 @@ type JWT struct {
 	expiry time.Duration
 
 	blacklist Blacklist
+	stopOnce  sync.Once
 	done      chan struct{}
 }
 
@@ -85,6 +87,7 @@ func New(expiry time.Duration, blacklist Blacklist, secret io.Reader) (*JWT, err
 	return jwt, nil
 }
 
+// sum calculates the HMAC hash sum of the token
 func (jwt *JWT) sum(token string, h Hash) []byte {
 	mac := hmac.New(h.Hash, jwt.key)
 	mac.Write([]byte(token))
@@ -248,8 +251,7 @@ func (jwt *JWT) Verify(t *Token) error {
 		nbfOK = true
 	}
 	if jwt.blacklist != nil {
-		err := jwt.blacklisted(t.Sig())
-		if err != nil {
+		if err := jwt.blacklisted(t.Sig()); err != nil {
 			return err
 		}
 	}
@@ -266,106 +268,12 @@ func (jwt *JWT) Verify(t *Token) error {
 }
 
 // Stop will end the cleaner goroutinge execution
-// Calling Stop twice or more will panic
 func (jwt *JWT) Stop() error {
 	if jwt.blacklist == nil {
 		return ErrBlacklistNotEnabled
 	}
-	close(jwt.done)
+	jwt.stopOnce.Do(func() {
+		close(jwt.done)
+	})
 	return nil
 }
-
-// DecodeToken decodes a raw string token into a *Token object
-func DecodeToken(token string) (t *Token, err error) {
-	if token == "" {
-		return nil, ErrEmptyToken
-	}
-	parts := strings.Split(token, ".")
-	if len(parts) < 3 {
-		return nil, ErrMissingTokenParts
-	}
-	if len(parts) > 3 {
-		return nil, ErrNoJWT
-	}
-	for _, v := range parts {
-		if v == "" {
-			return nil, ErrNoJWT
-		}
-	}
-	t = new(Token)
-	header, err := base64.URLEncoding.DecodeString(parts[0])
-	if err != nil {
-		return
-	}
-	err = json.Unmarshal(header, &t.header)
-	if err != nil {
-		return
-	}
-	claims, err := base64.URLEncoding.DecodeString(parts[1])
-	if err != nil {
-		return
-	}
-	err = json.Unmarshal(claims, &t.Claims)
-	if err != nil {
-		return
-	}
-	t.rawSignature, err = base64.URLEncoding.DecodeString(parts[2])
-	t.signature = parts[2]
-	t.data = strings.Join(parts[:2], ".")
-	t.raw = token
-	return
-}
-
-// Token is the JWT token representation
-type Token struct {
-	raw          string
-	data         string
-	signature    string
-	rawSignature []byte
-	header       map[string]interface{}
-	Claims       Claims
-}
-
-// String returns the tokens encoded string
-func (t *Token) String() string {
-	return t.raw
-}
-
-// Sig returns the Tokens URLEncoded signature
-func (t *Token) Sig() string {
-	return t.signature
-}
-
-// RawSig returns the Tokens raw signature
-func (t *Token) RawSig() []byte {
-	return t.rawSignature
-}
-
-// Header returns the Tokens header
-func (t *Token) Header() map[string]interface{} {
-	return t.header
-}
-
-// Data returns the first two token fields
-func (t *Token) Data() string {
-	return t.data
-}
-
-// NewToken returns a new *Token using the provided hash algorithm and claims
-// If claims is nil, an empty map is used
-// If hash is nil, HS256 is used
-func NewToken(claims Claims, hash Hash) *Token {
-	if claims == nil {
-		claims = make(Claims)
-	}
-	if hash == nil {
-		hash = NewHS256()
-	}
-	return &Token{
-		header: map[string]interface{}{
-			"alg": hash.Alg(),
-			"typ": typ,
-		},
-		Claims: claims,
-	}
-}
diff --git a/jwt_test.go b/jwt_test.go
index 17a519b..103eb32 100644
--- a/jwt_test.go
+++ b/jwt_test.go
@@ -58,6 +58,11 @@ func TestValidate(t *testing.T) {
 	if err != nil {
 		t.Error(err)
 	}
+	// should not panic
+	err = jwt.Stop()
+	if err != nil {
+		t.Error(err)
+	}
 }
 
 func TestNoBlacklist(t *testing.T) {
diff --git a/token.go b/token.go
new file mode 100644
index 0000000..3a08da2
--- /dev/null
+++ b/token.go
@@ -0,0 +1,104 @@
+// Copyright (C) 2018 Marius Schellenberger
+
+package jwt
+
+import (
+	"encoding/base64"
+	"encoding/json"
+	"strings"
+)
+
+// Token is the JWT token representation
+type Token struct {
+	raw          string
+	data         string
+	signature    string
+	rawSignature []byte
+	header       map[string]interface{}
+	Claims       Claims
+}
+
+// String returns the tokens encoded string
+func (t *Token) String() string {
+	return t.raw
+}
+
+// Sig returns the Tokens URLEncoded signature
+func (t *Token) Sig() string {
+	return t.signature
+}
+
+// RawSig returns the Tokens raw signature
+func (t *Token) RawSig() []byte {
+	return t.rawSignature
+}
+
+// Header returns the Tokens header
+func (t *Token) Header() map[string]interface{} {
+	return t.header
+}
+
+// Data returns the first two token fields
+func (t *Token) Data() string {
+	return t.data
+}
+
+// NewToken returns a new *Token using the provided hash algorithm and claims
+// If claims is nil, an empty map is used
+// If hash is nil, HS256 is used
+func NewToken(claims Claims, hash Hash) *Token {
+	if claims == nil {
+		claims = make(Claims)
+	}
+	if hash == nil {
+		hash = NewHS256()
+	}
+	return &Token{
+		header: map[string]interface{}{
+			"alg": hash.Alg(),
+			"typ": typ,
+		},
+		Claims: claims,
+	}
+}
+
+// DecodeToken decodes a raw string token into a *Token object
+func DecodeToken(token string) (t *Token, err error) {
+	if token == "" {
+		return nil, ErrEmptyToken
+	}
+	parts := strings.Split(token, ".")
+	if len(parts) < 3 {
+		return nil, ErrMissingTokenParts
+	}
+	if len(parts) > 3 {
+		return nil, ErrNoJWT
+	}
+	for _, v := range parts {
+		if v == "" {
+			return nil, ErrNoJWT
+		}
+	}
+	t = new(Token)
+	header, err := base64.URLEncoding.DecodeString(parts[0])
+	if err != nil {
+		return
+	}
+	err = json.Unmarshal(header, &t.header)
+	if err != nil {
+		return
+	}
+	claims, err := base64.URLEncoding.DecodeString(parts[1])
+	if err != nil {
+		return
+	}
+	err = json.Unmarshal(claims, &t.Claims)
+	if err != nil {
+		return
+	}
+	t.rawSignature, err = base64.URLEncoding.DecodeString(parts[2])
+	t.signature = parts[2]
+	t.data = strings.Join(parts[:2], ".")
+	t.raw = token
+	return
+}