diff --git a/src/wutil.h b/src/wutil.h
index 84a77e668..6c27666fd 100644
--- a/src/wutil.h
+++ b/src/wutil.h
@@ -8,6 +8,10 @@
 #include <stddef.h>
 #include <stdint.h>
 #include <sys/types.h>
+#ifdef __APPLE__
+// This include is required on macOS 10.10 for locale_t
+#include <xlocale.h>
+#endif
 
 #include <ctime>
 #include <functional>