diff --git a/include/mio/mmap.hpp b/include/mio/mmap.hpp
index def559a..40f2981 100644
--- a/include/mio/mmap.hpp
+++ b/include/mio/mmap.hpp
@@ -97,7 +97,7 @@ struct basic_mmap
     // user provided it, but we must close it if we obtained it using the
     // provided path. For this reason, this flag is used to determine when to
     // close `file_handle_`.
-    bool is_handle_internal_;
+    bool is_handle_internal_{false};
 
 public:
     /**