diff --git a/io.cpp b/io.cpp
index 3e6be2fe..68a191ff 100644
--- a/io.cpp
+++ b/io.cpp
@@ -231,8 +231,8 @@ scoped_cwd::~scoped_cwd ()
 
 
 ///////////////////////////////////////////////////////////////////////////////
-path_error::path_error (const std::filesystem::path &_path):
-    runtime_error (to_string (format::printf ("Unknown path: %!", m_path))),
+path_error::path_error (std::filesystem::path const &_path):
+    runtime_error (to_string (format::printf ("Unknown path: %!", _path))),
     m_path (_path)
 { ; }