diff --git a/ext/readline/config.m4 b/ext/readline/config.m4
index 58d21765c14..da1359ee9cd 100644
--- a/ext/readline/config.m4
+++ b/ext/readline/config.m4
@@ -10,7 +10,7 @@ if test "$PHP_LIBEDIT" = "no"; then
   [  --with-readline[=DIR]   Include readline support (CLI/CGI only)])
 fi
 
-if test "$PHP_READLINE" != "no"; then
+if test "$PHP_READLINE" && test "$PHP_READLINE" != "no"; then
   for i in $PHP_READLINE /usr/local /usr; do
     test -f $i/include/readline/readline.h && READLINE_DIR=$i && break
   done