diff --git a/config.m4 b/config.m4
index 9e9b5e1..ac18332 100755
--- a/config.m4
+++ b/config.m4
@@ -5,7 +5,7 @@ PHP_ARG_WITH(lua-version, to specify a custom lua version, [  --with-lua-version
 
 if test "$PHP_LUA" != "no"; then
   if test -r $PHP_LUA/include/lua.h; then
-    LUA_INCLUDE_DIR=$PHP_LUA
+    LUA_INCLUDE_DIR=$PHP_LUA/include
   else
     AC_MSG_CHECKING(for lua in default path)
     for i in /usr/local /usr; do