diff --git a/src/wp-includes/class-wp-http-requests-hooks.php b/src/wp-includes/class-wp-http-requests-hooks.php
index 108fae8c10..6650d5869c 100644
--- a/src/wp-includes/class-wp-http-requests-hooks.php
+++ b/src/wp-includes/class-wp-http-requests-hooks.php
@@ -54,7 +54,7 @@ class WP_HTTP_Requests_Hooks extends Requests_Hooks {
 		switch ( $hook ) {
 			case 'curl.before_send':
 				/** This action is documented in wp-includes/class-wp-http-curl.php */
-				do_action_ref_array( 'http_api_curl', array( $parameters[0], $this->request, $this->url ) );
+				do_action_ref_array( 'http_api_curl', array( &$parameters[0], $this->request, $this->url ) );
 				break;
 		}
 
diff --git a/tests/phpunit/tests/http/curl.php b/tests/phpunit/tests/http/curl.php
index b9481ed6cb..f3f80cd264 100644
--- a/tests/phpunit/tests/http/curl.php
+++ b/tests/phpunit/tests/http/curl.php
@@ -8,4 +8,19 @@ require_once dirname( __FILE__ ) . '/base.php';
  */
 class Tests_HTTP_curl extends WP_HTTP_UnitTestCase {
 	var $transport = 'curl';
+
+	/**
+	 * @ticket 39783
+	 */
+	public function test_http_api_curl_stream_parameter_is_a_reference() {
+		add_action( 'http_api_curl', array( $this, '_action_test_http_api_curl_stream_parameter_is_a_reference' ), 10, 3 );
+		wp_remote_request( $this->fileStreamUrl, array( 'stream' => true, 'timeout' => 30 ) );
+		remove_action( 'http_api_curl', array( $this, '_action_test_http_api_curl_stream_parameter_is_a_reference' ), 10 );
+	}
+
+	public function _action_test_http_api_curl_stream_parameter_is_a_reference( &$stream, $r, $url ) {
+		// $stream not being a reference will cause a PHP warning.
+		// For counting tests purposes, let's do a fake assert.
+		$this->assertTrue( true );
+	}
 }