diff --git a/include/cxxopts.hpp b/include/cxxopts.hpp
index abfd80d..e39ca51 100644
--- a/include/cxxopts.hpp
+++ b/include/cxxopts.hpp
@@ -40,6 +40,7 @@ THE SOFTWARE.
 #include <utility>
 #include <vector>
 #include <algorithm>
+#include <locale>
 
 #ifdef CXXOPTS_NO_EXCEPTIONS
 #include <iostream>