diff -Nru origsrc/zsh-5.8/Src/zsh_system.h src/zsh-5.8/Src/zsh_system.h
--- origsrc/zsh-5.8/Src/zsh_system.h	2020-02-15 07:06:57.000000000 +0900
+++ src/zsh-5.8/Src/zsh_system.h	2020-06-04 02:39:07.698004100 +0900
@@ -848,6 +848,10 @@
 #ifdef __CYGWIN__
 # include <sys/cygwin.h>
 # define IS_DIRSEP(c) ((c) == '/' || (c) == '\\')
+/* Cygwin Hack!  newlib doesn't define STDC ISO 10646, so hack it here */
+# if defined(HAVE_WCHAR_H) && defined(HAVE_WCTOMB) && !defined(__STDC_ISO_10646__)
+#  define __STDC_ISO_10646__
+# endif
 #else
 # define IS_DIRSEP(c) ((c) == '/')
 #endif