diff --git a/example/server/storage/storage.go b/example/server/storage/storage.go
index b687a2c..1bc2e94 100644
--- a/example/server/storage/storage.go
+++ b/example/server/storage/storage.go
@@ -615,12 +615,19 @@ func (s *Storage) renewRefreshToken(currentRefreshToken string) (string, string,
 	}
 	// deletes the refresh token
 	delete(s.refreshTokens, currentRefreshToken)
+
 	// delete the access token which was issued based on this refresh token
 	delete(s.tokens, refreshToken.AccessToken)
+
+	if refreshToken.Expiration.Before(time.Now()) {
+		return "", "", fmt.Errorf("expired refresh token")
+	}
+
 	// creates a new refresh token based on the current one
 	token := uuid.NewString()
 	refreshToken.Token = token
 	refreshToken.ID = token
+	refreshToken.Expiration = time.Now().Add(5 * time.Hour)
 	s.refreshTokens[token] = refreshToken
 	return token, refreshToken.ID, nil
 }