diff --git a/twitter.install b/twitter.install
index d83d6b4..c6cbcb7 100644
--- a/twitter.install
+++ b/twitter.install
@@ -377,14 +377,16 @@ function twitter_update_7301() {
  * Adds field mentions to twitter_account table.
  */
 function twitter_update_7400() {
-  $data = array(
-    'description' => "Boolean flag indicating whether the {twitter_user}'s mentions should be pulled in by the site.",
-    'type' => 'int',
-    'unsigned' => TRUE,
-    'not null' => TRUE,
-    'default' => 0,
-  );
-  db_add_field('twitter_account', 'mentions', $data);
+  if (db_field_exists('twitter_account', 'mentions') === FALSE) {
+    $data = array(
+      'description' => "Boolean flag indicating whether the {twitter_user}'s mentions should be pulled in by the site.",
+      'type' => 'int',
+      'unsigned' => TRUE,
+      'not null' => TRUE,
+      'default' => 0,
+    );
+    db_add_field('twitter_account', 'mentions', $data);
+  }
 }
 
 /**