diff --git a/m4/set-prefix.m4 b/m4/set-prefix.m4
index 6121172c551303cff4df9268f1d74ac513dbf0a0..bb7568659b4436a04b7b5fdb0b6f6d392fc22515 100644
--- a/m4/set-prefix.m4
+++ b/m4/set-prefix.m4
@@ -4,4 +4,8 @@ AC_DEFUN(AC_SET_PREFIX,
 [test "x$prefix" = xNONE && prefix=$ac_default_prefix
 # Let make expand exec_prefix.
 test "x$exec_prefix" = xNONE && exec_prefix='${prefix}'
+expanded_prefix=`eval echo ${prefix}`
+AC_SUBST(expanded_prefix)
+expanded_exec_prefix=`eval echo ${exec_prefix}`
+AC_SUBST(expanded_exec_prefix)
 ])