diff -ur ucon64/src/misc/ioapi.h ucon64.patched/src/misc/ioapi.h
--- ucon64/src/misc/ioapi.h	2016-03-03 22:55:44.000000000 +0900
+++ ucon64.patched/src/misc/ioapi.h	2020-12-02 01:36:03.624826600 +0900
@@ -35,6 +35,11 @@
 extern "C" {
 #endif
 
+// On NetBSD and Gentoo, OF is not defined in zconf.h, which is included by zlib.h.
+#ifndef OF
+#define OF(x) x
+#endif
+
 typedef voidpf (ZCALLBACK *open_file_func) OF((voidpf opaque, const char* filename, int mode));
 typedef uLong  (ZCALLBACK *read_file_func) OF((voidpf opaque, voidpf stream, void* buf, uLong size));
 typedef uLong  (ZCALLBACK *write_file_func) OF((voidpf opaque, voidpf stream, const void* buf, uLong size));
diff -ur ucon64/src/misc/unzip.h ucon64.patched/src/misc/unzip.h
--- ucon64/src/misc/unzip.h	2018-04-21 14:55:52.000000000 +0900
+++ ucon64.patched/src/misc/unzip.h	2020-12-02 01:36:17.657629200 +0900
@@ -49,7 +49,7 @@
 extern "C" {
 #endif
 
-// On NetBSD, OF is not defined in zconf.h, which is included by zlib.h.
+// On NetBSD and Gentoo, OF is not defined in zconf.h, which is included by zlib.h.
 #ifndef OF
 #define OF(x) x
 #endif