diff --git a/Makefile.am b/Makefile.am
index 386506c92..f25c0f068 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -24,7 +24,7 @@ pixmap_DATA = htop.png
 appicondir = $(datadir)/icons/hicolor/scalable/apps
 appicon_DATA = htop.svg
 
-AM_CFLAGS += -D_XOPEN_SOURCE_EXTENDED -DSYSCONFDIR="\"$(sysconfdir)\"" -I"$(top_srcdir)/$(my_htop_platform)"
+AM_CFLAGS += -DSYSCONFDIR="\"$(sysconfdir)\"" -I"$(top_srcdir)/$(my_htop_platform)"
 AM_LDFLAGS =
 
 myhtopsources = \
@@ -508,11 +508,11 @@ cppcheck:
 	cppcheck -q -v . --enable=all -DHAVE_OPENVZ
 
 dist-hook: $(top_distdir)/configure
-	@if test "x$$FORCE_MAKE_DIST" = x && \
-	   grep 'pkg_m4_absent' '$(top_distdir)/configure' >/dev/null; then \
-	   echo 'ERROR: This distribution would have incomplete pkg-config support. Rebuilding the configure script is advised. Set FORCE_MAKE_DIST=1 to ignore this warning.'>&2; \
+	@if test "x$$FORCE_MAKE_DIST" != x || \
+	   grep 'pkg_m4_included' '$(top_distdir)/configure' >/dev/null; then :; \
+	else \
+	   echo 'ERROR: The configure script has incomplete pkg-config support and regenerating it is advised. Set FORCE_MAKE_DIST=1 to ignore this warning.'>&2; \
 	   (exit 1); \
-	else :; \
 	fi
 	@if grep 'PACKAGE_VERSION.*-g' '$(top_distdir)/configure'; then \
 	  echo 'WARNING: You are building a dist from a git version. Better run make dist outside of a .git repo on a tagged release.'>&2; \
diff --git a/ProvideCurses.h b/ProvideCurses.h
index 7ae99e620..4594e3baf 100644
--- a/ProvideCurses.h
+++ b/ProvideCurses.h
@@ -8,7 +8,11 @@ in the source distribution for its full text.
 */
 
 
+// This header is also used in tests by configure, thus conditionally
+// including "config.h".
+#if defined(HAVE_CONFIG_H)
 #include "config.h" // IWYU pragma: keep
+#endif
 
 // IWYU pragma: begin_exports
 
diff --git a/configure.ac b/configure.ac
index 54f6e0e28..b20ff18fa 100644
--- a/configure.ac
+++ b/configure.ac
@@ -68,6 +68,22 @@ esac
 # Enable extensions, required by hwloc scripts
 AC_USE_SYSTEM_EXTENSIONS
 
+# The header of ncurses exposes wide-character interfaces only if
+# _XOPEN_SOURCE_EXTENDED is defined or _XOPEN_SOURCE defined to be
+# >= 500. In DragonFly BSD, FreeBSD and OpenBSD, defining
+# _XOPEN_SOURCE to any value *hides* interfaces that would be useful
+# for htop.
+dnl
+dnl Note: The "#undef" in AH_VERBATIM will be replaced with "#define"
+dnl when config.h is generated.
+AH_VERBATIM([_XOPEN_SOURCE_EXTENDED],
+[/* Enables XPG4v2 (SUSv1) interfaces if they are not enabled already with _XOPEN_SOURCE */
+#ifndef _XOPEN_SOURCE_EXTENDED
+#undef _XOPEN_SOURCE_EXTENDED
+#endif
+])
+AC_DEFINE([_XOPEN_SOURCE_EXTENDED], 1)
+
 # Activate some more of the missing global defines
 AC_SYS_LARGEFILE
 
@@ -384,8 +400,8 @@ dnl If the macro is not called, some pkg-config checks might be skipped
 dnl and $PKG_CONFIG might be unset.
 m4_ifdef([PKG_PROG_PKG_CONFIG], [
    PKG_PROG_PKG_CONFIG()
+   pkg_m4_included=1 # Makefile might grep this keyword. Don't remove.
 ], [
-   pkg_m4_absent=1 # Makefile might grep this keyword. Don't remove.
    m4_warn(
       [syntax],
       [pkg.m4 is absent or older than version 0.16; this 'configure' would have incomplete pkg-config support])
@@ -412,10 +428,10 @@ AC_ARG_WITH([curses],
             [],
             [with_curses=check])
 case $with_curses in
-check)
+check|yes)
    : # No-op. Use default list.
    ;;
-yes|no)
+no)
    AC_MSG_ERROR([bad value '$with_curses' for --with-curses option])
    ;;
 *)
@@ -450,18 +466,17 @@ htop_check_curses_capability () {
    # At this point we have not checked the name of curses header, so
    # use forward declaration for the linking tests below.
 
-   # htop uses keypad() and "stdscr", but for ncurses implementation,
-   # the symbols are in "-ltinfo" and not "-lncurses".
+   # htop uses keypad(), but for ncurses implementation, the symbol is
+   # in "-ltinfo" and not "-lncurses".
    # Check "-ltinfo" symbols first, as libncurses might require
    # explicit "-ltinfo" to link (for internal dependency).
    AC_MSG_CHECKING([for keypad in $htop_msg_linker_flags])
    AC_LINK_IFELSE([AC_LANG_PROGRAM([[
-/* extern WINDOW* stdscr; */
 /* int keypad(WINDOW* win, bool enable); */
-extern void* stdscr;
 int keypad(void* win, int enable);
       ]], [[
-keypad(stdscr, 0);
+static char dummy;
+keypad((void*)&dummy, 0);
       ]])],
       [AC_MSG_RESULT(yes)],
       [AC_MSG_RESULT(no)
@@ -483,13 +498,17 @@ doupdate();
          htop_curses_status=1])
    fi
 
+   # htop calls mvadd_wchnstr(), which might be implemented as a macro.
+   # It is more reliable to test linking with wadd_wchnstr().
    if test "x$htop_curses_status$enable_unicode" = x0yes; then
-      AC_MSG_CHECKING([for mvadd_wchnstr in $htop_msg_linker_flags])
+      AC_MSG_CHECKING([for wadd_wchnstr in $htop_msg_linker_flags])
       AC_LINK_IFELSE([AC_LANG_PROGRAM([[
-/* int mvadd_wchnstr(int y, int x, const cchar_t* wchstr, int n); */
-int mvadd_wchnstr(int y, int x, const void* wchstr, int n);
+/* int wadd_wchnstr(WINDOW* win, const cchar_t* wchstr, int n); */
+int wadd_wchnstr(void* win, const void* wchstr, int n);
          ]], [[
-mvadd_wchnstr(0, 0, (void*)0, 0);
+static char dummy1;
+static char dummy2;
+wadd_wchnstr((void*)&dummy1, (void*)&dummy2, 0);
          ]])],
          [AC_MSG_RESULT(yes)
          htop_curses_capability=wide],
@@ -607,7 +626,11 @@ none-*|nonwide-yes)
       for d in $list; do
          result=`find "$d" -name '*curses*.pc' 2>/dev/null | sed '1 q'`
          if test "x$result" != x; then
+            echo detected a .pc file: "$result" >&AS_MESSAGE_LOG_FD
             AC_MSG_WARN([your system supports pkg-config; installing pkg-config is recommended before configuring htop])
+            m4_ifdef([PKG_PROG_PKG_CONFIG], [], [
+               AC_MSG_WARN([this configure script would also need to be regenerated])
+            ])
             break
          fi
       done
@@ -643,6 +666,7 @@ esac
 
 htop_save_CFLAGS=$CFLAGS
 CFLAGS="$AM_CFLAGS $CFLAGS"
+
 if test "x$enable_unicode" = xyes; then
    AC_CHECK_HEADERS([ncursesw/curses.h], [],
       [AC_CHECK_HEADERS([ncurses/ncurses.h], [],
@@ -665,6 +689,34 @@ else
       [AC_CHECK_HEADERS([term.h], [],
          [AC_MSG_ERROR([can not find required term header file])])])
 fi
+
+CFLAGS="-I$srcdir $CFLAGS"
+
+# Check for things that might be macros.
+# "stdscr" is a macro in ncursest (reentrant version of ncurses).
+AC_MSG_CHECKING([whether the curses header works])
+AC_LINK_IFELSE([AC_LANG_PROGRAM([[
+/* Checks if the "bool" definition in curses is ISO C compatible */
+#include <stdbool.h>
+
+#include "ProvideCurses.h"
+   ]], [[
+keypad(stdscr, false);
+
+refresh();
+
+#if defined(HAVE_LIBNCURSESW)
+{
+   static cchar_t dummy;
+   mvadd_wchnstr(0, 0, &dummy, 0);
+}
+#endif
+   ]])],
+   [AC_MSG_RESULT(yes)],
+   [AC_MSG_RESULT(no)
+   AC_MSG_FAILURE([there are problems with the curses header])]
+)
+
 CFLAGS=$htop_save_CFLAGS
 
 if test "$enable_static" = yes; then