--- ckcasc.h
+++ ckcasc.h
@@ -42,7 +42,7 @@
 #define SYN   22        /* SYN, Ctrl-V */
 #define ETB   23        /* Ctrl-W */
 #define CAN   24        /* CAN, Ctrl-X */
-#define EM    25        /* Ctrl-Y */
+#define _EM   25        /* Ctrl-Y */
 #define SUB   26        /* SUB Ctrl-Z */
 #define ESC   27        /* Escape Ctrl-[ */
 #define XFS   28        /* Field Separator,  Ctrl-Backslash */