diff --git a/ext/mbstring/config.m4 b/ext/mbstring/config.m4
index ba76165bfcd..ab2b80b7b5d 100644
--- a/ext/mbstring/config.m4
+++ b/ext/mbstring/config.m4
@@ -34,7 +34,7 @@ AC_DEFUN([PHP_MBSTRING_EXTENSION], [
     PHP_ADD_BUILD_DIR([$ext_builddir/$dir])
   done
   
-  if test "$ext_shared" = "no" || ! test -e "$ext_builddir/config.h.in"; then
+  if test "$ext_shared" = "no" -o -e "$ext_builddir/config.h.in"; then
     out="php_config.h"
   else
     out="$abs_builddir/config.h"