diff --git a/acinclude.m4.in b/acinclude.m4.in
index bae2eac..a3e031b 100644
--- a/acinclude.m4.in
+++ b/acinclude.m4.in
@@ -3948,7 +3948,7 @@ AC_CANONICAL_SYSTEM
 AC_ARG_PROGRAM
 AM_INIT_AUTOMAKE($1, $2)
 AM_DISABLE_LIBRARIES
-AC_PREFIX_DEFAULT(${TDEDIR:-/usr/local/kde})
+AC_PREFIX_DEFAULT(${TDEDIR:-/opt/trinity})
 AC_CHECK_COMPILERS
 KDE_PROG_LIBTOOL
 AM_KDE_WITH_NLS
@@ -5440,12 +5440,12 @@ AC_DEFUN([KDE_CONF_FILES],
 
 dnl This sets the prefix, for arts and tdelibs
 dnl Do NOT use in any other module.
-dnl It only looks at --prefix, TDEDIR and falls back to /usr/local/kde
+dnl It only looks at --prefix, TDEDIR and falls back to /opt/trinity
 AC_DEFUN([KDE_SET_PREFIX_CORE],
 [
   unset CDPATH
   dnl make $TDEDIR the default for the installation
-  AC_PREFIX_DEFAULT(${TDEDIR:-/usr/local/kde})
+  AC_PREFIX_DEFAULT(${TDEDIR:-/opt/trinity})
 
   if test "x$prefix" = "xNONE"; then
     prefix=$ac_default_prefix