diff --git a/src/Control/Director.php b/src/Control/Director.php
index 316148578..2f42c8c5c 100644
--- a/src/Control/Director.php
+++ b/src/Control/Director.php
@@ -263,7 +263,7 @@ class Director implements TemplateGlobalProvider
         $newVars = HTTPRequestBuilder::cleanEnvironment($newVars);
 
         // Create new request
-        $request = HTTPRequestBuilder::createFromVariables($newVars, $body);
+        $request = HTTPRequestBuilder::createFromVariables($newVars, $body, ltrim($url, '/'));
         if ($headers) {
             foreach ($headers as $k => $v) {
                 $request->addHeader($k, $v);
diff --git a/src/Control/HTTPRequestBuilder.php b/src/Control/HTTPRequestBuilder.php
index 378ea3b10..0e81fc712 100644
--- a/src/Control/HTTPRequestBuilder.php
+++ b/src/Control/HTTPRequestBuilder.php
@@ -28,16 +28,20 @@ class HTTPRequestBuilder
      *
      * @param array $variables
      * @param string $input Request body
+     * @param string|null $url Provide specific url (relative to base)
      * @return HTTPRequest
      */
-    public static function createFromVariables(array $variables, $input)
+    public static function createFromVariables(array $variables, $input, $url = null)
     {
-        // Remove query parameters (they're retained separately through $server['_GET']
-        $url = parse_url($variables['_SERVER']['REQUEST_URI'], PHP_URL_PATH);
+        // Infer URL from REQUEST_URI unless explicitly provided
+        if (!isset($url)) {
+            // Remove query parameters (they're retained separately through $server['_GET']
+            $url = parse_url($variables['_SERVER']['REQUEST_URI'], PHP_URL_PATH);
 
-        // Remove base folders from the URL if webroot is hosted in a subfolder
-        if (substr(strtolower($url), 0, strlen(BASE_URL)) === strtolower(BASE_URL)) {
-            $url = substr($url, strlen(BASE_URL));
+            // Remove base folders from the URL if webroot is hosted in a subfolder
+            if (substr(strtolower($url), 0, strlen(BASE_URL)) === strtolower(BASE_URL)) {
+                $url = substr($url, strlen(BASE_URL));
+            }
         }
 
         // Build request
diff --git a/src/includes/constants.php b/src/includes/constants.php
index 61592cadf..a53ee8c0d 100644
--- a/src/includes/constants.php
+++ b/src/includes/constants.php
@@ -95,6 +95,11 @@ if (!defined('BASE_URL')) {
             return rtrim(parse_url($base, PHP_URL_PATH), '/');
         }
 
+        // Unless specified, use empty string for base in CLI
+        if (in_array(php_sapi_name(), ['cli', 'phpdbg'])) {
+            return "";
+        }
+
         // Determine the base URL by comparing SCRIPT_NAME to SCRIPT_FILENAME and getting common elements
         // This tends not to work on CLI
         $path = realpath($_SERVER['SCRIPT_FILENAME']);
diff --git a/tests/php/Control/DirectorTest.php b/tests/php/Control/DirectorTest.php
index fa3237545..b629317ce 100644
--- a/tests/php/Control/DirectorTest.php
+++ b/tests/php/Control/DirectorTest.php
@@ -929,4 +929,30 @@ class DirectorTest extends SapphireTest
     {
         $this->assertTrue(Director::is_cli(), 'is_cli should be true for PHP CLI and phpdbg');
     }
+
+    public function testMockRequest()
+    {
+        Director::config()->set('alternate_base_url', 'http://www.mysite.com/some-subdir/');
+
+        // Can handle root-relative $url
+        Director::mockRequest(function (HTTPRequest $request) {
+            $this->assertEquals('some-page/nested', $request->getURL());
+            $this->assertEquals(1, $request->getVar('query'));
+            $this->assertEquals('/some-subdir/some-page/nested', $_SERVER['REQUEST_URI']);
+        }, '/some-subdir/some-page/nested?query=1');
+
+        // Can handle absolute $url
+        Director::mockRequest(function (HTTPRequest $request) {
+            $this->assertEquals('some-page/nested', $request->getURL());
+            $this->assertEquals(1, $request->getVar('query'));
+            $this->assertEquals('/some-subdir/some-page/nested', $_SERVER['REQUEST_URI']);
+        }, 'http://www.mysite.com/some-subdir/some-page/nested?query=1');
+
+        // Can handle relative $url
+        Director::mockRequest(function (HTTPRequest $request) {
+            $this->assertEquals('some-page/nested', $request->getURL());
+            $this->assertEquals(1, $request->getVar('query'));
+            $this->assertEquals('/some-subdir/some-page/nested', $_SERVER['REQUEST_URI']);
+        }, 'some-page/nested?query=1');
+    }
 }