diff --git a/js/pmd/history.js b/js/pmd/history.js
index 8570d7d29e..302d8a6aa9 100644
--- a/js/pmd/history.js
+++ b/js/pmd/history.js
@@ -512,7 +512,7 @@ function query_groupby()
             str += history_array[i].get_column_name() + ", ";
         }
     }
-    str = str.substr(0, str.length - 1);
+    str = str.substr(0, str.length - 2);
     return str;
 }