diff --git a/arm9/source/date.h b/arm9/source/date.h
index d2f037e..4eb7dae 100644
--- a/arm9/source/date.h
+++ b/arm9/source/date.h
@@ -2,6 +2,7 @@
 #define DATE_H
 
 #include <string>
+#include <sys/types.h>
 
 /**
  * Format the time as specified.