diff --git src/wp-includes/feed.php src/wp-includes/feed.php
index dbeb3a0..59eb0db 100644
--- src/wp-includes/feed.php
+++ src/wp-includes/feed.php
@@ -503,6 +503,36 @@ function atom_enclosure() {
 		if ($key == 'enclosure') {
 			foreach ( (array) $val as $enc ) {
 				$enclosure = explode("\n", $enc);
+
+	                        $url    = '';
+        	                $length = 0;
+                	        $type   = '';
+
+	                        $mimes = get_allowed_mime_types();
+
+	                        // Parse url
+        	                if ( isset( $enclosure[0] ) && is_string( $enclosure[0] ) ) {
+                	                $url = trim( $enclosure[0] );
+                        	}
+
+	                        // Parse length and type
+        	                foreach( range( 1, 2 ) as $i ) {
+                	                if ( isset( $enclosure[$i] ) ) {
+                        	                if( is_numeric( $enclosure[$i] ) ) {
+                                	                $length = trim( $enclosure[$i] );
+                                        	} elseif ( in_array( $enclosure[$i], $mimes ) ) {
+                                                	$type = trim( $enclosure[$i] );
+	                                        }
+        	                        }
+                	        }
+                        
+				$html_link_tag = sprintf(
+                                	"<link href=\"%s\" rel=\"enclosure\" length=\"%d\" type=\"%s\" />\n",
+                                	esc_url ( $url ),
+                                	esc_attr( $length ),
+                                	esc_attr( $type )
+	                        );
+	
 				/**
 				 * Filters the atom enclosure HTML link tag for the current post.
 				 *
@@ -510,7 +540,7 @@ function atom_enclosure() {
 				 *
 				 * @param string $html_link_tag The HTML link tag with a URI and other attributes.
 				 */
-				echo apply_filters( 'atom_enclosure', '<link href="' . trim( htmlspecialchars( $enclosure[0] ) ) . '" rel="enclosure" length="' . trim( $enclosure[1] ) . '" type="' . trim( $enclosure[2] ) . '" />' . "\n" );
+	                         echo apply_filters( 'atom_enclosure', $html_link_tag );
 			}
 		}
 	}
diff --git tests/phpunit/tests/feed/atom.php tests/phpunit/tests/feed/atom.php
index fbe064b..7298b23 100644
--- tests/phpunit/tests/feed/atom.php
+++ tests/phpunit/tests/feed/atom.php
@@ -197,4 +197,78 @@ class Tests_Feeds_Atom extends WP_UnitTestCase {
 			}
 		}
 	}
+
+        /**
+         * @test 33591
+         */
+        function test_atom_enclosure_with_extended_url_length_type_parsing()
+        {
+                $enclosures = array(
+                        array(
+                                'actual'        => "https://wordpress.dev/wp-content/uploads/2017/09/movie.mp4\n318465\nvideo/mp4",     // url length type
+                                'expected'      => array(
+                                        'href'          => "https://wordpress.dev/wp-content/uploads/2017/09/movie.mp4",
+                                        'length'        => 318465,
+                                        'type'          => "video/mp4"
+                                )
+                        ),
+                        array(
+                                'actual'        => "https://wordpress.dev/wp-content/uploads/2017/09/movie.mp4\nvideo/mp4\n318465",     // url type length
+                                'expected'      => array(
+                                        'href'          => "https://wordpress.dev/wp-content/uploads/2017/09/movie.mp4",
+                                        'length'        => 318465,
+                                        'type'          => "video/mp4"
+                                )
+                        ),
+                        array(
+                                'actual'        => "https://wordpress.dev/wp-content/uploads/2017/09/movie.mp4\n318465",                // url length
+                                'expected'      => array(
+                                        'href'          => "https://wordpress.dev/wp-content/uploads/2017/09/movie.mp4",
+                                        'length'        => 318465,
+                                        'type'          => ""
+                                )
+                        ),
+                        array(
+                                'actual'        => "https://wordpress.dev/wp-content/uploads/2017/01/audio.mp3\n\naudio/mpeg",          // url type
+                                'expected'      => array(
+                                        'href'          => "https://wordpress.dev/wp-content/uploads/2017/01/audio.mp3",
+                                        'length'        => 0,
+                                        'type'          => "audio/mpeg"
+                                )
+                        ),
+                        array(
+                                'actual'        => "https://wordpress.dev/wp-content/uploads/2016/01/test.mp4",                         // url
+                                'expected'      => array(
+                                        'href'          => "https://wordpress.dev/wp-content/uploads/2016/01/test.mp4",
+                                        'length'        => 0,
+                                        'type'          => ""
+                                )
+                        ),
+                );
+
+                $post_id = end( self::$posts );
+                foreach( $enclosures as $enclosure ) {
+                        add_post_meta( $post_id, 'enclosure', $enclosure['actual'] );
+                }
+                $this->go_to( '/?feed=atom' );
+                $feed = $this->do_atom();
+                $xml = xml_to_array( $feed );
+                $entries = xml_find( $xml, 'feed', 'entry' );
+                $entries = array_slice( $entries, 0, 1 );
+
+                foreach ( $entries as $key => $entry ) {
+                        $links = xml_find( $entries[$key]['child'], 'link' );
+			$i = 0;
+                        foreach ( (array) $links as $link ) {
+                                if ( 'enclosure' == $link['attributes']['rel'] ) {
+                                        $this->assertEquals( $enclosures[$i]['expected']['href'] , $link['attributes']['href'] );
+                                        $this->assertEquals( $enclosures[$i]['expected']['length'] , $link['attributes']['length'] );
+                                        $this->assertEquals( $enclosures[$i]['expected']['type'] , $link['attributes']['type'] );
+                                        $i++;
+                                }
+                        }
+                }
+        }
+
+
 }