diff --git a/Util/BoostFileSystemFix.h b/Util/BoostFileSystemFix.h
index 1e1e98e0e..99b325fc6 100644
--- a/Util/BoostFileSystemFix.h
+++ b/Util/BoostFileSystemFix.h
@@ -121,7 +121,7 @@ portable_canonical(const boost::filesystem::path &relative_path,
 inline path temp_directory_path()
 {
     char *buffer;
-    buffer = tmpnam(NULL);
+    buffer = tmpnam(nullptr);
 
     return path(buffer);
 }