diff --git a/lib/util.php b/lib/util.php
index 0e3af013d5..a953fa39a8 100644
--- a/lib/util.php
+++ b/lib/util.php
@@ -183,7 +183,9 @@ function common_show_header($pagetitle, $callable=NULL, $data=NULL, $headercall=
 	common_element_start('div', array('id' => 'wrap'));
 	common_element_start('div', array('id' => 'header'));
 	common_nav_menu();
-	if ($config['site']['logo'] || file_exists(theme_file('logo.png'))) {
+	if ((is_string($config['site']['logo']) && (strlen($config['site']['logo']) > 0))
+		|| file_exists(theme_file('logo.png')))
+	{
 		common_element_start('a', array('href' => common_local_url('public')));
 		common_element('img', array('src' => ($config['site']['logo']) ?
 									($config['site']['logo']) : theme_path('logo.png'),