diff --git a/geolocation.install b/geolocation.install
index a456a3e..1a17438 100644
--- a/geolocation.install
+++ b/geolocation.install
@@ -56,7 +56,7 @@ function geolocation_field_schema($field) {
   $indexes = array(
     'lat' => array('lat'),
     'lng' => array('lng'),
-    'lng' => array('altitude'),
+    'altitude' => array('altitude'),
   );
   return array(
     'columns' => $columns,