diff --git a/cmd/jwt/main.go b/cmd/jwt/main.go
index 6ab3b94f..af2607e6 100644
--- a/cmd/jwt/main.go
+++ b/cmd/jwt/main.go
@@ -192,7 +192,7 @@ func signToken() error {
 	// add command line claims
 	if len(flagClaims) > 0 {
 		for k, v := range flagClaims {
-			claims[k] = v
+			claims[jwt.ClaimsType(k)] = v
 		}
 	}
 
diff --git a/map_claims.go b/map_claims.go
index 3b920527..0a519519 100644
--- a/map_claims.go
+++ b/map_claims.go
@@ -5,44 +5,55 @@ import (
 	"fmt"
 )
 
+type ClaimsType string
+
+var (
+	Exp ClaimsType = "exp"
+	Nbf ClaimsType = "nbf"
+	Iat ClaimsType = "iat"
+	Aud ClaimsType = "aud"
+	Iss ClaimsType = "iss"
+	Sub ClaimsType = "sub"
+)
+
 // MapClaims is a claims type that uses the map[string]any for JSON
 // decoding. This is the default claims type if you don't supply one
-type MapClaims map[string]any
+type MapClaims map[ClaimsType]any
 
 // GetExpirationTime implements the Claims interface.
 func (m MapClaims) GetExpirationTime() (*NumericDate, error) {
-	return m.parseNumericDate("exp")
+	return m.parseNumericDate(Exp)
 }
 
 // GetNotBefore implements the Claims interface.
 func (m MapClaims) GetNotBefore() (*NumericDate, error) {
-	return m.parseNumericDate("nbf")
+	return m.parseNumericDate(Nbf)
 }
 
 // GetIssuedAt implements the Claims interface.
 func (m MapClaims) GetIssuedAt() (*NumericDate, error) {
-	return m.parseNumericDate("iat")
+	return m.parseNumericDate(Iat)
 }
 
 // GetAudience implements the Claims interface.
 func (m MapClaims) GetAudience() (ClaimStrings, error) {
-	return m.parseClaimsString("aud")
+	return m.parseClaimsString(Aud)
 }
 
 // GetIssuer implements the Claims interface.
 func (m MapClaims) GetIssuer() (string, error) {
-	return m.parseString("iss")
+	return m.parseString(Iss)
 }
 
 // GetSubject implements the Claims interface.
 func (m MapClaims) GetSubject() (string, error) {
-	return m.parseString("sub")
+	return m.parseString(Sub)
 }
 
 // parseNumericDate tries to parse a key in the map claims type as a number
 // date. This will succeed, if the underlying type is either a [float64] or a
 // [json.Number]. Otherwise, nil will be returned.
-func (m MapClaims) parseNumericDate(key string) (*NumericDate, error) {
+func (m MapClaims) parseNumericDate(key ClaimsType) (*NumericDate, error) {
 	v, ok := m[key]
 	if !ok {
 		return nil, nil
@@ -66,7 +77,7 @@ func (m MapClaims) parseNumericDate(key string) (*NumericDate, error) {
 
 // parseClaimsString tries to parse a key in the map claims type as a
 // [ClaimsStrings] type, which can either be a string or an array of string.
-func (m MapClaims) parseClaimsString(key string) (ClaimStrings, error) {
+func (m MapClaims) parseClaimsString(key ClaimsType) (ClaimStrings, error) {
 	var cs []string
 	switch v := m[key].(type) {
 	case string:
@@ -89,7 +100,7 @@ func (m MapClaims) parseClaimsString(key string) (ClaimStrings, error) {
 // parseString tries to parse a key in the map claims type as a [string] type.
 // If the key does not exist, an empty string is returned. If the key has the
 // wrong type, an error is returned.
-func (m MapClaims) parseString(key string) (string, error) {
+func (m MapClaims) parseString(key ClaimsType) (string, error) {
 	var (
 		ok  bool
 		raw any
diff --git a/map_claims_test.go b/map_claims_test.go
index e055b33f..00add68b 100644
--- a/map_claims_test.go
+++ b/map_claims_test.go
@@ -142,7 +142,7 @@ func TestMapClaimsVerifyExpiresAtExpire(t *testing.T) {
 
 func TestMapClaims_parseString(t *testing.T) {
 	type args struct {
-		key string
+		key ClaimsType
 	}
 	tests := []struct {
 		name    string