Index: wp-includes/comment-template.php
===================================================================
--- wp-includes/comment-template.php	(revision 40242)
+++ wp-includes/comment-template.php	(working copy)
@@ -1376,7 +1376,11 @@
 
 			$top_level_count = $top_level_query->query( $top_level_args );
 
-			$comment_args['offset'] = ( ceil( $top_level_count / $per_page ) - 1 ) * $per_page;
+			if ( $top_level_count && $per_page ) {
+				$comment_args['offset'] = ( ceil( $top_level_count / $per_page ) - 1 ) * $per_page;
+			} else {
+				$comment_args['offset'] = 0;
+			}
 		}
 	}