configure: Don't enable maintainer mode if it is explicitly not requested.
diff --git a/configure.ac b/configure.ac
index 4c0cdbe..8d2dffe 100644
--- a/configure.ac
+++ b/configure.ac
@@ -25,8 +25,7 @@
 AC_ARG_ENABLE(win16, AS_HELP_STRING([--disable-win16],[do not include Win16 support]))
 AC_ARG_ENABLE(win64, AS_HELP_STRING([--enable-win64],[build a Win64 emulator on AMD64 (won't run Win32 binaries)]))
 AC_ARG_ENABLE(tests, AS_HELP_STRING([--disable-tests],[do not build the regression tests]))
-AC_ARG_ENABLE(maintainer-mode, AS_HELP_STRING([--enable-maintainer-mode],[enable maintainer-specific build rules]),
-                               ,[AC_SUBST([MAINTAINER_MODE],[\#])])
+AC_ARG_ENABLE(maintainer-mode, AS_HELP_STRING([--enable-maintainer-mode],[enable maintainer-specific build rules]))
 
 AC_ARG_WITH(alsa,      AS_HELP_STRING([--without-alsa],[do not use the Alsa sound support]),
             [if test "x$withval" = "xno"; then ac_cv_header_sys_asoundlib_h=no; ac_cv_header_alsa_asoundlib_h=no; fi])
@@ -286,8 +285,10 @@
 AC_CHECK_PROGS(CONVERT, convert, false)
 AC_CHECK_PROGS(ICOTOOL, icotool, false)
 
-if test "${enable_maintainer_mode+set}" = set
+if test "x$enable_maintainer_mode" != "xyes"
 then
+  AC_SUBST([MAINTAINER_MODE],[\#])
+else
   if test "$FONTFORGE" = "false"; then WINE_WARNING([fontforge is missing, fonts can't be rebuilt.]); fi
   if test "$RSVG" = "false"; then WINE_WARNING([rsvg is missing, icons can't be rebuilt.]); fi
 
@@ -1610,7 +1611,7 @@
   fi
 
   dnl Enable -Werror for maintainer mode
-  if test "${enable_maintainer_mode+set}" = set
+  if test "x$enable_maintainer_mode" = "xyes"
   then
       WINE_TRY_CFLAGS([-Werror])
   fi