diff --git a/curses.h b/curses.h
index 39d54c5f..65c1db1a 100644
--- a/curses.h
+++ b/curses.h
@@ -100,6 +100,12 @@ typedef chtype attr_t;
  *
  */
 
+#if _LP64
+typedef unsigned int mmask_t;
+#else
+typedef unsigned long mmask_t;
+#endif
+
 typedef struct
 {
     int x;           /* absolute column, 0 based, measured in characters */
@@ -206,8 +212,6 @@ typedef struct
 
 /* ncurses mouse interface */
 
-typedef unsigned long mmask_t;
-
 typedef struct
 {
     short id;       /* unused, always 0 */