diff --git a/aegisub/libaegisub/lagi_pre.h b/aegisub/libaegisub/lagi_pre.h
index 545cfe945..6e342944a 100644
--- a/aegisub/libaegisub/lagi_pre.h
+++ b/aegisub/libaegisub/lagi_pre.h
@@ -28,6 +28,7 @@
 #include <fstream>
 #include <iostream>
 #include <iterator>
+#include <locale>
 #include <numeric>
 #include <map>
 #include <sstream>