diff --git a/cake/libs/inflector.php b/cake/libs/inflector.php
index 46fc540be..dc0f78f6b 100644
--- a/cake/libs/inflector.php
+++ b/cake/libs/inflector.php
@@ -369,7 +369,10 @@ class Inflector {
 						} else {
 							$_this->{$var}[$rule] = array_merge($pattern, $_this->{$var}[$rule]);
 						}
-						unset($rules[$rule], $_this->{$var}['cache' . ucfirst($rule)], $_this->{$var}['merged'][$rule]);
+						unset($rules[$rule], $_this->{$var}['cache' . ucfirst($rule)]);
+						if (isset($_this->{$var}['merged'][$rule])) {
+							unset($_this->{$var}['merged'][$rule]);
+						}
 						if ($type === 'plural') {
 							$_this->_pluralized = $_this->_tableize = array();
 						} elseif ($type === 'singular') {
diff --git a/cake/tests/cases/libs/inflector.test.php b/cake/tests/cases/libs/inflector.test.php
index c894e8a65..519b39978 100644
--- a/cake/tests/cases/libs/inflector.test.php
+++ b/cake/tests/cases/libs/inflector.test.php
@@ -42,16 +42,6 @@ class InflectorTest extends CakeTestCase {
  */
 	var $Inflector = null;
 
-/**
- * setUp method
- *
- * @access public
- * @return void
- */
-	function setUp() {
-		$this->Inflector = Inflector::getInstance();
-	}
-
 /**
  * testInstantiation method
  *
@@ -59,7 +49,8 @@ class InflectorTest extends CakeTestCase {
  * @return void
  */
 	function testInstantiation() {
-		$this->assertEqual(Inflector::getInstance(), $this->Inflector);
+		$Inflector =& Inflector::getInstance();
+		$this->assertEqual(Inflector::getInstance(), $Inflector);
 	}
 
 /**
@@ -339,6 +330,19 @@ class InflectorTest extends CakeTestCase {
 		$this->assertEqual(Inflector::humanize('file_systems'), 'File Systems');
 	}
 
+/**
+ * This test if run in isolation should not cause errors in PHP4.
+ *
+ * @return void
+ */
+	function testRulesNoErrorPHP4() {
+		Inflector::rules('plural', array(
+			'rules' => array(),
+			'irregular' => array(),
+			'uninflected' => array('pays')
+		));
+	}
+
 /**
  * testCustomPluralRule method
  *
@@ -455,13 +459,4 @@ class InflectorTest extends CakeTestCase {
 		$this->assertEqual(Inflector::singularize('Atlas'), 'Atlas');
 	}
 
-/**
- * tearDown method
- *
- * @access public
- * @return void
- */
-	function tearDown() {
-		unset($this->Inflector);
-	}
 }