diff --git a/leaflet.formatters.inc b/leaflet.formatters.inc
index 1c53a21..e091623 100644
--- a/leaflet.formatters.inc
+++ b/leaflet.formatters.inc
@@ -588,7 +588,7 @@ function leaflet_form_elements($group, $settings, $options = NULL) {
         '#type' => 'select',
         '#title' => t('Marker field'),
         '#description' => t('Field to use as output for a map marker.'),
-        '#options' => array_merge(array('' => ''), $options['fields']),
+        '#options' => (array)array_merge(array('' => ''), $options['fields']),
         '#default_value' => isset($settings[$group]['html']) ? $settings[$group]['html'] : '',
         '#empty_option' => t('-- Select --'),
         '#states' => array(