diff --git a/configure.ac b/configure.ac
index 1ec6eb4..9e47feb 100644
--- a/configure.ac
+++ b/configure.ac
@@ -487,7 +487,7 @@ AM_CONDITIONAL([HAVE_P11KIT], [test "x$have_p11kit" = "xyes"])
 
 # check for --prefix and set flag HAVE_PREFIX if found
 #   do not change install location if --prefix is given and with P11_KIT found
-AM_CONDITIONAL([HAVE_PREFIX], [test ! -z "$(prefix)"])
+AM_CONDITIONAL([HAVE_PREFIX], [test ! -z "${prefix}"])
 
 # END P11 CONFIG