diff --git a/fmt/posix.cc b/fmt/posix.cc
index 49fcb395..f96e2c14 100644
--- a/fmt/posix.cc
+++ b/fmt/posix.cc
@@ -65,7 +65,7 @@ inline std::size_t convert_rwcount(std::size_t count) { return count; }
 std::FILE* u8fopen(fmt::CStringRef filename, fmt::CStringRef mode) {
 #ifdef _WIN32
   fmt::UTF8ToUTF16 nconv(filename.c_str());
-  fmt::UTF8ToUTF16 mconv(filename.c_str());
+  fmt::UTF8ToUTF16 mconv(mode.c_str());
   return FMT_SYSTEM(_wfopen(nconv.c_str(), mconv.c_str()));
 #else
   return FMT_SYSTEM(fopen(filename.c_str(), mode.c_str()));