diff --git a/src/modb_database_p.c b/src/modb_database_p.c
index d854aec..cb97e32 100644
--- a/src/modb_database_p.c
+++ b/src/modb_database_p.c
@@ -304,7 +304,8 @@ uint64_t createMDOGroupsTable(stored_conn *sconn, modb_ref *modb)
         "`mdo_id` INT UNSIGNED NOT NULL, "
         "`group_id` INT UNSIGNED NOT NULL, "
         "INDEX(`mdo_id`), "
-        "INDEX(`group_id`)"
+        "INDEX(`group_id`), "
+        "UNIQUE(`mdo_id`, `group_id`)"
         ")", 0
         );
 }
@@ -352,7 +353,8 @@ uint64_t createUserGroupsTable(stored_conn *sconn, modb_ref *modb)
         "`user_id` INT UNSIGNED NOT NULL, "
         "`group_id` INT UNSIGNED NOT NULL, "
         "INDEX(`user_id`), "
-        "INDEX(`group_id`)"
+        "INDEX(`group_id`),"
+        "UNIQUE(`user_id`, `group_id`)"
         ")", 0
         );
 }
@@ -375,7 +377,7 @@ uint64_t createMetaExtTable(stored_conn *sconn, modb_ref *modb,
     strbld_str(sb, ", ", 2);
     columnCreateStr_sb(sb, *(col_data + c));
   }
-  strbld_str(sb, ", INDEX (`mdo_id`)"
+  strbld_str(sb, ", PRIMARY KEY (`mdo_id`)"
                  ")", 0);
   if (strbld_finalize_or_destroy(&sb, &table_def, &table_def_len) != 0) {
     return (uint64_t)-1;