Index: libcxx/trunk/src/filesystem/operations.cpp
===================================================================
--- libcxx/trunk/src/filesystem/operations.cpp
+++ libcxx/trunk/src/filesystem/operations.cpp
@@ -439,7 +439,8 @@
   return posix_lstat(p, path_stat, ec);
 }
 
-bool posix_ftruncate(const FileDescriptor& fd, size_t to_size, error_code& ec) {
+// http://pubs.opengroup.org/onlinepubs/9699919799/functions/ftruncate.html
+bool posix_ftruncate(const FileDescriptor& fd, off_t to_size, error_code& ec) {
   if (::ftruncate(fd.fd, to_size) == -1) {
     ec = capture_errno();
     return true;