diff -ruN a/configure b/configure
--- a/configure	2026-06-06 04:54:35.000000000 -0500
+++ b/configure	2026-06-08 21:43:31.051165555 -0500
@@ -12623,6 +12623,7 @@
 ###   use option --enable-widec to turn on use of wide-character support
 NCURSES_CH_T=chtype
 NCURSES_LIBUTF8=0
+NCURSES_WIDECHAR=0
 
 NEED_WCHAR_H=0
 NCURSES_MBSTATE_T=0
@@ -12862,6 +12863,7 @@
 #define NCURSES_WIDECHAR 1
 EOF
 
+	NCURSES_WIDECHAR=1
 	case "$CPPFLAGS" in
 	(*_XOPEN_SOURCE=*)
 		;;
@@ -30784,6 +30786,7 @@
 s,@NCURSES_WCWIDTH_GRAPHICS@,$NCURSES_WCWIDTH_GRAPHICS,;t t
 s,@NCURSES_CH_T@,$NCURSES_CH_T,;t t
 s,@NCURSES_LIBUTF8@,$NCURSES_LIBUTF8,;t t
+s,@NCURSES_WIDECHAR@,$NCURSES_WIDECHAR,;t t
 s,@NEED_WCHAR_H@,$NEED_WCHAR_H,;t t
 s,@NCURSES_MBSTATE_T@,$NCURSES_MBSTATE_T,;t t
 s,@NCURSES_WCHAR_T@,$NCURSES_WCHAR_T,;t t
diff -ruN a/configure.in b/configure.in
--- a/configure.in	2026-05-30 14:20:26.000000000 -0500
+++ b/configure.in	2026-06-08 21:43:31.043165313 -0500
@@ -880,6 +880,7 @@
 ###   use option --enable-widec to turn on use of wide-character support
 NCURSES_CH_T=chtype
 NCURSES_LIBUTF8=0
+NCURSES_WIDECHAR=0
 
 NEED_WCHAR_H=0
 NCURSES_MBSTATE_T=0
@@ -912,6 +913,7 @@
 	fi
 	AC_DEFINE(USE_WIDEC_SUPPORT,1,[Define to 1 to compile with wide character and UTF-8 support])
 	AC_DEFINE(NCURSES_WIDECHAR,1,[Define to 1 to compile with wide character and UTF-8 support])
+	NCURSES_WIDECHAR=1
 	case "$CPPFLAGS" in
 	(*_XOPEN_SOURCE=*)
 		;;
@@ -945,6 +947,7 @@
 fi
 AC_SUBST(NCURSES_CH_T)
 AC_SUBST(NCURSES_LIBUTF8)
+AC_SUBST(NCURSES_WIDECHAR)
 
 AC_SUBST(NEED_WCHAR_H)
 AC_SUBST(NCURSES_MBSTATE_T)
diff -ruN a/include/MKterm.h.awk.in b/include/MKterm.h.awk.in
--- a/include/MKterm.h.awk.in	2025-12-26 17:33:14.000000000 -0600
+++ b/include/MKterm.h.awk.in	2026-06-08 21:54:26.409799414 -0500
@@ -126,14 +126,14 @@
 	print  "#undef  SET_TTY"
 	print  "#undef  GET_TTY"
 	print  ""
-	print  "#if @HAVE_TERMIOS_H@ && @HAVE_TCGETATTR@	/* #if HAVE_TERMIOS_H && HAVE_TCGETATTR */"
+	print  "#if HAVE_TERMIOS_H && HAVE_TCGETATTR	/* #if HAVE_TERMIOS_H && HAVE_TCGETATTR */"
 	print  ""
 	print  "#undef  TERMIOS"
 	print  "#define TERMIOS 1"
 	print  "#include <termios.h>"
 	print  "#define TTY struct termios"
 	print  ""
-	print  "#elif @HAVE_TERMIO_H@	/* HAVE_TERMIO_H */"
+	print  "#elif HAVE_TERMIO_H	/* HAVE_TERMIO_H */"
 	print  ""
 	print  "#undef  TERMIOS"
 	print  "#define TERMIOS 1"
@@ -145,7 +145,7 @@
 	print  "#include <nc_win32.h>"
 	print  "#define TTY ConsoleMode"
 	print  ""
-	print  "#elif @HAVE_SGTTY_H@	/* HAVE_SGTTY_H */"
+	print  "#elif HAVE_SGTTY_H	/* HAVE_SGTTY_H */"
 	print  ""
 	print  "#undef TERMIOS"
 	print  "#include <sgtty.h>"
@@ -165,7 +165,7 @@
 	print  "#elif defined(_WIN32) || defined(_WIN64)"
 	print  "#define GET_TTY(fd, buf) _nc_console_getmode(_nc_console_fd2handle(fd),buf)"
 	print  "#define SET_TTY(fd, buf) _nc_console_setmode(_nc_console_fd2handle(fd),buf)"
-	print  "#elif @HAVE_SGTTY_H@	/* HAVE_SGTTY_H */"
+	print  "#elif HAVE_SGTTY_H	/* HAVE_SGTTY_H */"
 	print  "#define GET_TTY(fd, buf) gtty(fd, buf)"
 	print  "#define SET_TTY(fd, buf) stty(fd, buf)"
 	print  "#endif"
diff -ruN a/include/curses.h.in b/include/curses.h.in
--- a/include/curses.h.in	2026-05-30 14:13:55.000000000 -0500
+++ b/include/curses.h.in	2026-06-08 21:43:31.051165555 -0500
@@ -254,10 +254,14 @@
  * conflicting) when _XOPEN_SOURCE is 500 or greater.  If NCURSES_WIDECHAR is
  * not already defined, e.g., if the platform relies upon nonstandard feature
  * test macros, define it at this point if the standard feature test macros
- * indicate that it should be defined.
+ * indicate that it should be defined.  Prefer the configure-time result when
+ * generating the ncurses headers, so building a wide-character library does
+ * not depend on the host's feature-test macro policy.
  */
 #ifndef NCURSES_WIDECHAR
-#if defined(_XOPEN_SOURCE_EXTENDED) || (defined(_XOPEN_SOURCE) && (_XOPEN_SOURCE - 0 >= 500))
+#if @NCURSES_WIDECHAR@	/* NCURSES_WIDECHAR */
+#define NCURSES_WIDECHAR 1
+#elif defined(_XOPEN_SOURCE_EXTENDED) || (defined(_XOPEN_SOURCE) && (_XOPEN_SOURCE - 0 >= 500))
 #define NCURSES_WIDECHAR 1
 #else
 #define NCURSES_WIDECHAR 0
diff -ruN a/include/ncurses_cfg.hin b/include/ncurses_cfg.hin
--- a/include/ncurses_cfg.hin	2024-06-08 09:04:14.000000000 -0500
+++ b/include/ncurses_cfg.hin	2026-06-08 21:59:39.717239025 -0500
@@ -50,6 +50,55 @@
 #define NC_CONFIG_H
 @DEFS@
 
+/*
+ * Vertex builds ncurses as a Linux wide-character library.  Keep the private
+ * generated headers coherent when cross/sysroot feature probes are cached or
+ * skipped by the package manager.
+ */
+#ifndef SIG_ATOMIC_T
+#define SIG_ATOMIC_T volatile sig_atomic_t
+#endif
+
+#ifndef HAVE_TERMIOS_H
+#define HAVE_TERMIOS_H 1
+#endif
+
+#ifndef HAVE_TCGETATTR
+#define HAVE_TCGETATTR 1
+#endif
+
+#ifndef HAVE_LIMITS_H
+#define HAVE_LIMITS_H 1
+#endif
+
+#ifndef HAVE_UNISTD_H
+#define HAVE_UNISTD_H 1
+#endif
+
+#ifndef HAVE_MBLEN
+#define HAVE_MBLEN 1
+#endif
+
+#ifndef HAVE_MBTOWC
+#define HAVE_MBTOWC 1
+#endif
+
+#ifndef HAVE_MBRLEN
+#define HAVE_MBRLEN 1
+#endif
+
+#ifndef HAVE_MBRTOWC
+#define HAVE_MBRTOWC 1
+#endif
+
+#ifndef USE_WIDEC_SUPPORT
+#define USE_WIDEC_SUPPORT 1
+#endif
+
+#ifndef NCURSES_WIDECHAR
+#define NCURSES_WIDECHAR 1
+#endif
+
 #include <ncurses_def.h>
 
 	/* The C compiler may not treat these properly but C++ has to */
diff -ruN a/ncurses/base/lib_pad.c b/ncurses/base/lib_pad.c
--- a/ncurses/base/lib_pad.c	2024-12-07 11:44:59.000000000 -0600
+++ b/ncurses/base/lib_pad.c	2026-06-08 22:02:50.246305708 -0500
@@ -257,8 +257,8 @@
 		register struct ldat *pline = &CurScreen(sp)->_line[nind];
 		for (j = 0; j <= my_len; j++) {
 		    int k = NewScreen(sp)->_maxx - j;
-		    if (pline->text[j] != nline->text[j]
-			|| pline->text[k] != nline->text[k]) {
+		    if (!CharEq(pline->text[j], nline->text[j])
+			|| !CharEq(pline->text[k], nline->text[k])) {
 			nind = _NEWINDEX;
 			break;
 		    }