diff --git a/token/jwt/claims_id_token.go b/token/jwt/claims_id_token.go
index b560de6e..7c10844f 100644
--- a/token/jwt/claims_id_token.go
+++ b/token/jwt/claims_id_token.go
@@ -49,10 +49,29 @@ func (c *IDTokenClaims) ToMap() map[string]interface{} {
 		ret["jti"] = uuid.New().String()
 	}
 
+	if _, ok := ret["aud"].([]string); !ok {
+		if _, ok := ret["aud"].(string); ok {
+			ret["aud"] = []string{ret["aud"].(string)}
+		} else {
+			ret["aud"] = []string{}
+		}
+	}
+
 	if len(c.Audience) > 0 {
-		ret["aud"] = c.Audience
-	} else {
-		ret["aud"] = []string{}
+		newAuds := []string{}
+		m := map[string]struct{}{}
+		for _, a := range c.Audience {
+			m[a] = struct{}{}
+			newAuds = append(newAuds, a)
+		}
+
+		var extraAud = ret["aud"].([]string)
+		for _, aud := range extraAud {
+			if _, ok := m[aud]; !ok {
+				newAuds = append(newAuds, aud)
+			}
+		}
+		ret["aud"] = newAuds
 	}
 
 	if !c.IssuedAt.IsZero() {
diff --git a/token/jwt/claims_id_token_test.go b/token/jwt/claims_id_token_test.go
index e2dca9c6..f897e6c9 100644
--- a/token/jwt/claims_id_token_test.go
+++ b/token/jwt/claims_id_token_test.go
@@ -76,3 +76,53 @@ func TestIDTokenClaimsToMap(t *testing.T) {
 		"nonce":     idTokenClaims.Nonce,
 	}, idTokenClaims.ToMap())
 }
+
+func TestIDTokenClaimsToMap_new_aud(t *testing.T) {
+	// extra & overlap
+	IDClaims := &IDTokenClaims{
+		JTI:      "foo-id",
+		Audience: []string{"default"},
+		Extra: map[string]any{
+			"aud": []string{"default", "new"},
+		},
+	}
+	assert.Equal(t, map[string]any{
+		"jti": "foo-id",
+		"aud": []string{"default", "new"},
+	}, IDClaims.ToMap())
+
+	// extra & no original values
+	IDClaims = &IDTokenClaims{
+		JTI: "foo-id",
+		Extra: map[string]any{
+			"aud": []string{"default", "new"},
+		},
+	}
+	assert.Equal(t, map[string]any{
+		"jti": "foo-id",
+		"aud": []string{"default", "new"},
+	}, IDClaims.ToMap())
+
+	// only original values
+	IDClaims = &IDTokenClaims{
+		JTI:      "foo-id",
+		Audience: []string{"default"},
+	}
+	assert.Equal(t, map[string]any{
+		"jti": "foo-id",
+		"aud": []string{"default"},
+	}, IDClaims.ToMap())
+
+	// extra value is an string
+	IDClaims = &IDTokenClaims{
+		JTI:      "foo-id",
+		Audience: []string{"default"},
+		Extra: map[string]any{
+			"aud": "new",
+		},
+	}
+	assert.Equal(t, map[string]any{
+		"jti": "foo-id",
+		"aud": []string{"default", "new"},
+	}, IDClaims.ToMap())
+}