unireg.h:

  Max index key length increased from 1024 to 3072
  for 64 bit builds.

sql/unireg.h

@@ -50,7 +50,11 @@
 #define MAX_SYS_VAR_LENGTH 32
 #define MAX_KEY 64				/* Max used keys */
 #define MAX_REF_PARTS 16			/* Max parts used as ref */
-#define MAX_KEY_LENGTH 1024			/* max possible key */
+#if SIZEOF_CHARP > 4
+#define MAX_KEY_LENGTH 3072			/* max possible key, if 64 bits */
+#else
+#define MAX_KEY_LENGTH 1024			/* max possible key, if 32 bits */
+#endif
 #if SIZEOF_OFF_T > 4
 #define MAX_REFLENGTH 8				/* Max length for record ref */
 #else