diff --git a/jwt.go b/jwt.go
index 06995aa..36e58f4 100644
--- a/jwt.go
+++ b/jwt.go
@@ -19,13 +19,46 @@ var TimeFunc = time.Now
 // Header of the token (such as `kid`) to identify which key to use.
 type Keyfunc func(*Token) (interface{}, error)
 
+// For a type to be a Claims object, it must just have a Valid method that determines
+// if the token is invalid for any supported reason
+type Claims interface {
+	Valid() error
+}
+
+type MapClaim map[string]interface{}
+
+func (m MapClaim) Valid() error {
+	vErr := new(ValidationError)
+	now := TimeFunc().Unix()
+
+	if exp, ok := m["exp"].(float64); ok {
+		if now > int64(exp) {
+			vErr.err = "token is expired"
+			vErr.Errors |= ValidationErrorExpired
+		}
+	}
+
+	if nbf, ok := m["nbf"].(float64); ok {
+		if now < int64(nbf) {
+			vErr.err = "token is not valid yet"
+			vErr.Errors |= ValidationErrorNotValidYet
+		}
+	}
+
+	if vErr.valid() {
+		return nil
+	}
+
+	return vErr
+}
+
 // A JWT Token.  Different fields will be used depending on whether you're
 // creating or parsing/verifying a token.
 type Token struct {
 	Raw       string                 // The raw token.  Populated when you Parse a token
 	Method    SigningMethod          // The signing method used or to be used
 	Header    map[string]interface{} // The first segment of the token
-	Claims    map[string]interface{} // The second segment of the token
+	Claims    Claims                 // The second segment of the token
 	Signature string                 // The third segment of the token.  Populated when you Parse a token
 	Valid     bool                   // Is the token valid?  Populated when you Parse/Verify a token
 }
@@ -37,7 +70,7 @@ func New(method SigningMethod) *Token {
 			"typ": "JWT",
 			"alg": method.Alg(),
 		},
-		Claims: make(map[string]interface{}),
+		Claims: make(MapClaim),
 		Method: method,
 	}
 }
@@ -63,16 +96,15 @@ func (t *Token) SigningString() (string, error) {
 	var err error
 	parts := make([]string, 2)
 	for i, _ := range parts {
-		var source map[string]interface{}
-		if i == 0 {
-			source = t.Header
-		} else {
-			source = t.Claims
-		}
-
 		var jsonValue []byte
-		if jsonValue, err = json.Marshal(source); err != nil {
-			return "", err
+		if i == 0 {
+			if jsonValue, err = json.Marshal(t.Header); err != nil {
+				return "", err
+			}
+		} else {
+			if jsonValue, err = json.Marshal(t.Claims); err != nil {
+				return "", err
+			}
 		}
 
 		parts[i] = EncodeSegment(jsonValue)
@@ -130,20 +162,8 @@ func Parse(tokenString string, keyFunc Keyfunc) (*Token, error) {
 	}
 
 	// Check expiration times
-	vErr := &ValidationError{}
-	now := TimeFunc().Unix()
-	if exp, ok := token.Claims["exp"].(float64); ok {
-		if now > int64(exp) {
-			vErr.err = "token is expired"
-			vErr.Errors |= ValidationErrorExpired
-		}
-	}
-	if nbf, ok := token.Claims["nbf"].(float64); ok {
-		if now < int64(nbf) {
-			vErr.err = "token is not valid yet"
-			vErr.Errors |= ValidationErrorNotValidYet
-		}
-	}
+	err = token.Claims.Valid()
+	vErr := err.(ValidationError)
 
 	// Perform validation
 	if err = token.Method.Verify(strings.Join(parts[0:2], "."), parts[2], key); err != nil {