diff --git a/db.class.php b/db.class.php
index 29c978a..f222732 100644
--- a/db.class.php
+++ b/db.class.php
@@ -873,8 +873,8 @@ class WhereClause {
       $args = array_merge($args, $clause_args);
     }
     
-    if ($this->type == 'and') $sql = implode(' AND ', $sql);
-    else $sql = implode(' OR ', $sql);
+    if ($this->type == 'and') $sql = sprintf('(%s)', implode(' AND ', $sql));
+    else $sql = sprintf('(%s)', implode(' OR ', $sql));
     
     if ($this->negate) $sql = '(NOT ' . $sql . ')';
     return array($sql, $args);
diff --git a/simpletest/WhereClauseTest.php b/simpletest/WhereClauseTest.php
index 45843d1..14ceee7 100644
--- a/simpletest/WhereClauseTest.php
+++ b/simpletest/WhereClauseTest.php
@@ -58,7 +58,17 @@ class WhereClauseTest extends SimpleTest {
     $this->assert($result[0]['age'] === '15');
   }
 
-  function test_6_or() {
+  function test_6_negate_two() {
+    $where = new WhereClause('and');
+    $where->add('password=%s', 'hello');
+    $where->add('username=%s', 'Bart');
+    $where->negate();
+    
+    $result = DB::query("SELECT * FROM accounts WHERE %l", $where);
+    $this->assert(count($result) === 7);
+  }
+
+  function test_7_or() {
     $where = new WhereClause('or');
     $where->add('username=%s', 'Bart');
     $where->add('username=%s', 'Abe');