diff --git includes/layer_types/js/tms.js includes/layer_types/js/tms.js
index 3250c83..ba13a1b 100644
--- includes/layer_types/js/tms.js
+++ includes/layer_types/js/tms.js
@@ -9,6 +9,7 @@
  */
 Drupal.openlayers.layer.tms = function(title, map, options) {
   var styleMap = Drupal.openlayers.getStyleMap(map, options.drupalID);
+  options.isBaseLayer = options.baselayer;
     if (options.maxExtent !== undefined) {
       options.maxExtent = new OpenLayers.Bounds.fromArray(options.maxExtent);
     }
diff --git includes/layer_types/tms.inc includes/layer_types/tms.inc
index ad86f24..0136740 100644
--- includes/layer_types/tms.inc
+++ includes/layer_types/tms.inc
@@ -42,7 +42,7 @@ class openlayers_layer_type_tms extends openlayers_layer_type {
       'base_url' => array(
         '#type' => 'textfield',
         '#title' => t('Base URL'),
-        '#default_value' => isset($this->data['base_url']) ? 
+        '#default_value' => isset($this->data['base_url']) ?
           $this->data['base_url'] : ''
       ),
       'layername' => array(
@@ -51,6 +51,12 @@ class openlayers_layer_type_tms extends openlayers_layer_type {
         '#default_value' => isset($this->data['layername']) ?
           $this->data['layername'] : ''
       ),
+      'baselayer' => array(
+        '#type' => 'checkbox',
+        '#default_value' => $this->data['baselayer'],
+        '#title' => t('BaseLayer'),
+        '#description' => t('Uncheck to make this map an overlay')
+      ),
       'type' => array(
         '#type' => 'select',
         '#title' => t('File Format'),
@@ -83,7 +89,7 @@ class openlayers_layer_type_tms extends openlayers_layer_type {
    * Render.
    */
   function render(&$map) {
-    drupal_add_js(drupal_get_path('module', 'openlayers') 
+    drupal_add_js(drupal_get_path('module', 'openlayers')
       . '/includes/layer_types/js/tms.js');
     return $this->options;
   }