Index: src/wp-includes/canonical.php
===================================================================
--- src/wp-includes/canonical.php	(revision 57184)
+++ src/wp-includes/canonical.php	(working copy)
@@ -316,7 +316,7 @@
 					$redirect['query'] = remove_query_arg( 'year', $redirect['query'] );
 				}
 			}
-		} elseif ( is_author() && ! empty( $_GET['author'] ) && preg_match( '|^[0-9]+$|', $_GET['author'] ) ) {
+		} elseif ( is_author() && ! empty( $_GET['author'] ) && is_string( $_GET['author'] ) && preg_match( '|^[0-9]+$|', $_GET['author'] ) ) {
 			$author = get_userdata( get_query_var( 'author' ) );
 
 			if ( false !== $author
Index: tests/phpunit/tests/canonical.php
===================================================================
--- tests/phpunit/tests/canonical.php	(revision 57184)
+++ tests/phpunit/tests/canonical.php	(working copy)
@@ -206,6 +206,7 @@
 			array( '/?author=%d', '/author/canonical-author/' ),
 			// array( '/?author=%d&year=2008', '/2008/?author=3'),
 			// array( '/author/canonical-author/?year=2008', '/2008/?author=3'), // Either or, see previous testcase.
+			array( '/author/canonical-author/?author[1]=hello', '/author/canonical-author/?author[1]=hello' ),
 
 			// Feeds.
 			array( '/?feed=atom', '/feed/atom/' ),