diff --git a/httplib.h b/httplib.h
index 63e5e5a..c57fa31 100644
--- a/httplib.h
+++ b/httplib.h
@@ -622,7 +622,7 @@ public:
   Server &Options(const std::string &pattern, Handler handler);
 
   bool set_base_dir(const std::string &dir,
-                    const std::string &mount_point = nullptr);
+                    const std::string &mount_point = std::string());
   bool set_mount_point(const std::string &mount_point, const std::string &dir,
                        Headers headers = Headers());
   bool remove_mount_point(const std::string &mount_point);