diff --git a/src/fs.h b/src/fs.h
--- a/src/fs.h
+++ b/src/fs.h
@@ -106,6 +106,13 @@
     return p1;
 }
 
+// Disallow implicit std::string conversion for copy_file
+// to avoid locale-dependent encoding on Windows.
+static inline void copy_file(const path &from, const path &to,
+                             copy_option options) {
+    boost::filesystem::copy_file(from, to, options);
+}
+
 /**
  * Convert path object to byte string. On POSIX, paths natively are byte
  * strings so this is trivial. On Windows, paths natively are Unicode, so an