diff --git a/.gitattributes b/.gitattributes
index b4f0b6cbb44..93ab7e6c7c5 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -1,3 +1,36 @@
+# Line endings
+#
+# Checked out with LF everywhere, whatever core.autocrlf says locally.
+#
+# Without this, a Windows clone with core.autocrlf=true gets CRLF source, and
+# fifteen tests fail that pass everywhere else. They compare helper output
+# against a literal multi-line string written in the test file: the helpers
+# build their output from "\n" escapes, so they always emit LF, while the
+# expected value picks up whatever the file on disk uses. CRLF checkout, CRLF
+# expectation, LF actual, failure - in Form_helper_test, Html_helper_test and
+# Calendar_test.
+#
+# This only affects what lands in the working tree. Repository content is
+# unchanged, and PHP does not care either way, so nothing downstream breaks.
+* text=auto eol=lf
+
+# Windows-only files keep their native endings
+*.bat text eol=crlf
+
+# Binaries git should not touch at all
+*.png binary
+*.jpg binary
+*.jpeg binary
+*.gif binary
+*.ico binary
+*.woff binary
+*.woff2 binary
+*.ttf binary
+*.eot binary
+*.pdf binary
+*.zip binary
+*.gz binary
+
 # This file tells which files and directories should be ignored and
 # NOT downloaded when using composer to pull down a project with
 # the --prefer-dist option selected. Used to remove development
diff --git a/system/libraries/Form_validation.php b/system/libraries/Form_validation.php
index eeb83b99f0c..f8b848b4977 100644
--- a/system/libraries/Form_validation.php
+++ b/system/libraries/Form_validation.php
@@ -56,6 +56,23 @@ class CI_Form_validation {
 	 */
 	protected $CI;
 
+	/**
+	 * Object that callback_ rules are resolved against.
+	 *
+	 * NULL means the CodeIgniter instance, which is the historic behaviour and
+	 * is correct when callbacks live on the controller.
+	 *
+	 * This exists because $CI was doing two unrelated jobs: it is the handle
+	 * for core services (lang, uri, router, input) AND it was the only place a
+	 * callback could be looked up. Code that wanted callbacks somewhere other
+	 * than the controller had to overwrite $CI outright, which quietly broke
+	 * the services and made the callback target depend on whoever assigned
+	 * last. Setting this instead leaves $CI alone.
+	 *
+	 * @var object|null
+	 */
+	protected $_callback_object = NULL;
+
 	/**
 	 * Validation data for the current form submission
 	 *
@@ -152,6 +169,46 @@ public function __construct($rules = array())
 
 	// --------------------------------------------------------------------
 
+	/**
+	 * Set Callback Object
+	 *
+	 * Tells the validator where to look for callback_ rules. Without this the
+	 * only way to run callbacks on a model, a service or any other collaborator
+	 * is to overwrite $CI, which also hands it the job of supplying lang, uri,
+	 * router and input.
+	 *
+	 * The library is shared for the whole request, so set this immediately
+	 * before run() rather than once in a constructor - otherwise whoever
+	 * constructed last owns every callback lookup that follows.
+	 *
+	 * Pass NULL to go back to the CodeIgniter instance.
+	 *
+	 * @param	object|null	$object
+	 * @return	CI_Form_validation
+	 */
+	public function set_callback_object($object = NULL)
+	{
+		$this->_callback_object = is_object($object) ? $object : NULL;
+		return $this;
+	}
+
+	// --------------------------------------------------------------------
+
+	/**
+	 * Callback Object
+	 *
+	 * Where callback_ rules are resolved, defaulting to the CodeIgniter
+	 * instance so existing controllers are unaffected.
+	 *
+	 * @return	object
+	 */
+	public function callback_object()
+	{
+		return isset($this->_callback_object) ? $this->_callback_object : $this->CI;
+	}
+
+	// --------------------------------------------------------------------
+
 	/**
 	 * Set Rules
 	 *
@@ -713,7 +770,9 @@ protected function _execute($row, $rules, $postdata = NULL, $cycles = 0)
 			{
 				if ($callback)
 				{
-					if ( ! method_exists($this->CI, $rule))
+					$object = $this->callback_object();
+
+					if ( ! method_exists($object, $rule))
 					{
 						log_message('debug', 'Unable to find callback validation rule: '.$rule);
 						$result = FALSE;
@@ -721,7 +780,7 @@ protected function _execute($row, $rules, $postdata = NULL, $cycles = 0)
 					else
 					{
 						// Run the function and grab the result
-						$result = $this->CI->$rule($postdata, $param);
+						$result = $object->$rule($postdata, $param);
 					}
 				}
 				else
diff --git a/tests/codeigniter/libraries/Form_validation_test.php b/tests/codeigniter/libraries/Form_validation_test.php
index 7d941a93c09..6f502c5ed8f 100644
--- a/tests/codeigniter/libraries/Form_validation_test.php
+++ b/tests/codeigniter/libraries/Form_validation_test.php
@@ -604,6 +604,79 @@ public function test_encode_php_tags()
 		$this->assertEquals('?>', $this->form_validation->encode_php_tags('?>'));
 	}
 
+	// --------------------------------------------------------------------
+	// set_callback_object()
+	// --------------------------------------------------------------------
+
+	public function test_callback_object_defaults_to_the_ci_instance()
+	{
+		// The historic behaviour: callbacks live on the controller
+		$this->assertSame(
+			$this->ci_instance(),
+			$this->form_validation->callback_object()
+		);
+	}
+
+	public function test_set_callback_object_redirects_callback_lookup()
+	{
+		$this->form_validation->set_callback_object(new Form_validation_test_callbacks());
+
+		$this->assertTrue($this->run_rules(
+			array(array('field' => 'foo', 'label' => 'Foo', 'rules' => 'callback_is_the_word_ok')),
+			array('foo' => 'ok')
+		));
+
+		$this->assertFalse($this->run_rules(
+			array(array('field' => 'foo', 'label' => 'Foo', 'rules' => 'callback_is_the_word_ok')),
+			array('foo' => 'nope')
+		));
+	}
+
+	public function test_set_callback_object_leaves_the_ci_reference_alone()
+	{
+		// The point of the whole change. Overwriting $CI to move callbacks
+		// also took lang, uri, router and input with it.
+		$before = $this->ci_instance();
+
+		$this->form_validation->set_callback_object(new Form_validation_test_callbacks());
+
+		$this->assertSame($before, $this->ci_instance());
+		$this->assertNotSame($this->ci_instance(), $this->form_validation->callback_object());
+	}
+
+	public function test_set_callback_object_null_restores_the_ci_instance()
+	{
+		$this->form_validation->set_callback_object(new Form_validation_test_callbacks());
+		$this->form_validation->set_callback_object(NULL);
+
+		$this->assertSame($this->ci_instance(), $this->form_validation->callback_object());
+	}
+
+	public function test_set_callback_object_ignores_a_non_object()
+	{
+		$this->form_validation->set_callback_object('not an object');
+
+		$this->assertSame($this->ci_instance(), $this->form_validation->callback_object());
+	}
+
+	public function test_set_callback_object_is_chainable()
+	{
+		$this->assertSame(
+			$this->form_validation,
+			$this->form_validation->set_callback_object(new Form_validation_test_callbacks())
+		);
+	}
+
+	public function test_a_missing_callback_still_fails_rather_than_erroring()
+	{
+		$this->form_validation->set_callback_object(new Form_validation_test_callbacks());
+
+		$this->assertFalse($this->run_rules(
+			array(array('field' => 'foo', 'label' => 'Foo', 'rules' => 'callback_no_such_method')),
+			array('foo' => 'ok')
+		));
+	}
+
 	/**
 	 * Run rules
 	 *
@@ -627,3 +700,15 @@ public function run_rules($rules, $values)
 		return $valid;
 	}
 }
+
+/**
+ * A collaborator that is not the controller, which is the whole point of
+ * set_callback_object().
+ */
+class Form_validation_test_callbacks {
+
+	public function is_the_word_ok($str)
+	{
+		return $str === 'ok';
+	}
+}