diff --git a/libcxx/include/__config b/libcxx/include/__config
--- a/libcxx/include/__config
+++ b/libcxx/include/__config
@@ -1449,6 +1449,13 @@
 # define _LIBCPP_INIT_PRIORITY_MAX
 #endif
 
+#ifdef __GNUC__
+#  define _LIBCPP_PRINTFILE(fmtarg, firstvararg) \
+     __attribute__((__format__(__printf__, fmtarg, firstvararg)))
+#else
+#  define _LIBCPP_PRINTFILE(fmtarg, firstvararg)
+#endif
+
 #endif // __cplusplus
 
 #endif // _LIBCPP_CONFIG
diff --git a/libcxx/src/filesystem/directory_iterator.cpp b/libcxx/src/filesystem/directory_iterator.cpp
--- a/libcxx/src/filesystem/directory_iterator.cpp
+++ b/libcxx/src/filesystem/directory_iterator.cpp
@@ -272,7 +272,7 @@
     path root = move(__imp_->__root_);
     __imp_.reset();
     if (m_ec)
-      err.report(m_ec, "at root \"%s\"", root);
+      err.report(m_ec, "at root \"%s\"", root.c_str());
   }
   return *this;
 }
@@ -359,7 +359,7 @@
   if (m_ec) {
     path root = move(stack.top().__root_);
     __imp_.reset();
-    err.report(m_ec, "at root \"%s\"", root);
+    err.report(m_ec, "at root \"%s\"", root.c_str());
   } else {
     __imp_.reset();
   }
@@ -404,7 +404,7 @@
     } else {
       path at_ent = move(curr_it.__entry_.__p_);
       __imp_.reset();
-      err.report(m_ec, "attempting recursion into \"%s\"", at_ent);
+      err.report(m_ec, "attempting recursion into \"%s\"", at_ent.c_str());
     }
   }
   return false;
diff --git a/libcxx/src/filesystem/filesystem_common.h b/libcxx/src/filesystem/filesystem_common.h
--- a/libcxx/src/filesystem/filesystem_common.h
+++ b/libcxx/src/filesystem/filesystem_common.h
@@ -57,8 +57,8 @@
 
 namespace {
 
-static string format_string_imp(const char* msg, ...) {
-  // we might need a second shot at this, so pre-emptivly make a copy
+static _LIBCPP_PRINTFILE(1, 0) string
+    format_string_impl(const char* msg, va_list& args) {
   struct GuardVAList {
     va_list& target;
     bool active = true;
@@ -73,10 +73,9 @@
         va_end(target);
     }
   };
-  va_list args;
-  va_start(args, msg);
-  GuardVAList args_guard(args);
 
+  GuardVAList args_guard(args);
+  // we might need a second shot at this, so pre-emptivly make a copy
   va_list args_cp;
   va_copy(args_cp, args);
   GuardVAList args_copy_guard(args_cp);
@@ -103,22 +102,16 @@
   size_with_null = static_cast<size_t>(ret) + 1;
   result.__resize_default_init(size_with_null - 1);
   ret = ::vsnprintf(&result[0], size_with_null, msg, args);
+  args_guard.clear();
   _LIBCPP_ASSERT(static_cast<size_t>(ret) == (size_with_null - 1), "TODO");
 
   return result;
 }
 
-const path::value_type* unwrap(path::string_type const& s) { return s.c_str(); }
-const path::value_type* unwrap(path const& p) { return p.native().c_str(); }
-template <class Arg>
-Arg const& unwrap(Arg const& a) {
-  static_assert(!is_class<Arg>::value, "cannot pass class here");
-  return a;
-}
-
-template <class... Args>
-string format_string(const char* fmt, Args const&... args) {
-  return format_string_imp(fmt, unwrap(args)...);
+static _LIBCPP_PRINTFILE(1, 2) string format_string(const char* msg, ...) {
+  va_list args;
+  va_start(args, msg);
+  return format_string_impl(msg, args);
 }
 
 error_code capture_errno() {
@@ -190,14 +183,15 @@
     _LIBCPP_UNREACHABLE();
   }
 
-  template <class... Args>
-  T report(const error_code& ec, const char* msg, Args const&... args) const {
+  _LIBCPP_PRINTFILE(3, 0)
+  T report_impl(const error_code& ec, const char* msg, va_list& args) const {
     if (ec_) {
+      va_end(args);
       *ec_ = ec;
       return error_value<T>();
     }
     string what =
-        string("in ") + func_name_ + ": " + format_string(msg, args...);
+        string("in ") + func_name_ + ": " + format_string_impl(msg, args);
     switch (bool(p1_) + bool(p2_)) {
     case 0:
       __throw_filesystem_error(what, ec);
@@ -209,11 +203,20 @@
     _LIBCPP_UNREACHABLE();
   }
 
+  _LIBCPP_PRINTFILE(3, 4)
+  T report(const error_code& ec, const char* msg, ...) const {
+    va_list args;
+    va_start(args, msg);
+    return report_impl(ec, msg, args);
+  }
+
   T report(errc const& err) const { return report(make_error_code(err)); }
 
-  template <class... Args>
-  T report(errc const& err, const char* msg, Args const&... args) const {
-    return report(make_error_code(err), msg, args...);
+  _LIBCPP_PRINTFILE(3, 4)
+  T report(errc const& err, const char* msg, ...) const {
+    va_list args;
+    va_start(args, msg);
+    return report_impl(make_error_code(err), msg, args);
   }
 
 private:
diff --git a/libcxx/src/filesystem/operations.cpp b/libcxx/src/filesystem/operations.cpp
--- a/libcxx/src/filesystem/operations.cpp
+++ b/libcxx/src/filesystem/operations.cpp
@@ -1447,11 +1447,11 @@
   error_code m_ec;
   file_status st = detail::posix_stat(p, &m_ec);
   if (!status_known(st))
-    return err.report(m_ec, "cannot access path \"" PS_FMT "\"", p);
+    return err.report(m_ec, "cannot access path \"" PS_FMT "\"", p.c_str());
 
   if (!exists(st) || !is_directory(st))
-    return err.report(errc::not_a_directory, "path \"" PS_FMT "\" is not a directory",
-                      p);
+    return err.report(errc::not_a_directory,
+                      "path \"" PS_FMT "\" is not a directory", p.c_str());
 
   return p;
 }