diff --git a/example/example.go b/example/example.go
index 90b63cd..8156bae 100644
--- a/example/example.go
+++ b/example/example.go
@@ -47,11 +47,17 @@ func main() {
 		slogecho.AddCustomAttributes(c, slog.String("foo", "bar"))
 		return c.String(http.StatusOK, "Hello, World!")
 	})
-	e.GET("/error", func(c echo.Context) error {
+	e.GET("/error1", func(c echo.Context) error {
 		return echo.
 			NewHTTPError(http.StatusInternalServerError, "A simulated error").
 			WithInternal(errors.New("A simulated internal error"))
 	})
+	e.GET("/error2", func(c echo.Context) error {
+		return echo.NewHTTPError(http.StatusInternalServerError, "A simulated error")
+	})
+	e.GET("/error3", func(c echo.Context) error {
+		return errors.New("A simulated error")
+	})
 
 	// Start server
 	e.Logger.Fatal(e.Start(":4242"))
diff --git a/middleware.go b/middleware.go
index f81c54f..1534357 100644
--- a/middleware.go
+++ b/middleware.go
@@ -289,8 +289,11 @@ func NewWithConfig(logger *slog.Logger, config Config) echo.MiddlewareFunc {
 						"message":  httpErr.Message,
 						"internal": httpErr.Internal,
 					}),
-					slog.String("internal", httpErr.Internal.Error()),
 				)
+
+				if httpErr.Internal != nil {
+					attributes = append(attributes, slog.String("internal", httpErr.Internal.Error()))
+				}
 			}
 
 			logger.LogAttrs(c.Request().Context(), level, msg, attributes...)