diff --git a/includes/database/query.inc b/includes/database/query.inc
index c77968767..9cdd8784e 100644
--- a/includes/database/query.inc
+++ b/includes/database/query.inc
@@ -1704,9 +1704,6 @@ class DatabaseCondition implements QueryConditionInterface, Countable {
       if (is_array($value)) {
         $operator = 'IN';
       }
-      elseif (!isset($value)) {
-        $operator = 'IS NULL';
-      }
       else {
         $operator = '=';
       }
@@ -1740,7 +1737,7 @@ class DatabaseCondition implements QueryConditionInterface, Countable {
    * Implements QueryConditionInterface::isNull().
    */
   public function isNull($field) {
-    return $this->condition($field);
+    return $this->condition($field, NULL, 'IS NULL');
   }
 
   /**
diff --git a/modules/simpletest/tests/database_test.test b/modules/simpletest/tests/database_test.test
index 87d386aa7..91a51f361 100644
--- a/modules/simpletest/tests/database_test.test
+++ b/modules/simpletest/tests/database_test.test
@@ -1454,11 +1454,25 @@ class DatabaseSelectTestCase extends DatabaseTestCase {
   }
 
   /**
-   * Test that we can find a record with a NULL value.
+   * Test that a comparison with NULL is always FALSE.
    */
   function testNullCondition() {
     $this->ensureSampleDataNull();
 
+    $names = db_select('test_null', 'tn')
+      ->fields('tn', array('name'))
+      ->condition('age', NULL)
+      ->execute()->fetchCol();
+
+    $this->assertEqual(count($names), 0, t('No records found when comparing to NULL.'));
+  }
+
+  /**
+   * Test that we can find a record with a NULL value.
+   */
+  function testIsNullCondition() {
+    $this->ensureSampleDataNull();
+
     $names = db_select('test_null', 'tn')
       ->fields('tn', array('name'))
       ->isNull('age')
@@ -1471,7 +1485,7 @@ class DatabaseSelectTestCase extends DatabaseTestCase {
   /**
    * Test that we can find a record without a NULL value.
    */
-  function testNotNullCondition() {
+  function testIsNotNullCondition() {
     $this->ensureSampleDataNull();
 
     $names = db_select('test_null', 'tn')