diff --git a/mu4e/mu4e-headers.el b/mu4e/mu4e-headers.el
index 4369610d..a82abfe1 100644
--- a/mu4e/mu4e-headers.el
+++ b/mu4e/mu4e-headers.el
@@ -207,10 +207,10 @@ chronologically (`:date') by the newest message in the thread.")
 
 ;;;; Graph drawing
 
-(defvar mu4e-headers-thread-mark-as-orphan 'all
+(defvar mu4e-headers-thread-mark-as-orphan 'first
   "Define which messages should be prefixed with the orphan mark.
-`all' marks all the messages without a parent as orphan, `first' only
-marks the first message in the thread.")
+`all' marks all the messages without a parent as orphan, `first'
+only marks the first message in the thread.")
 
 (defvar mu4e-headers-thread-root-prefix '("* " . "□ ")
   "Prefix for root messages.")
@@ -457,9 +457,9 @@ with DOCID which must be present in the headers buffer."
                    (mu4e~headers-thread-prefix-map
                     (if single-orphan 'single-orphan
                       (if (and orphan
-			       (or first-child
-				   (not (eq mu4e-headers-thread-mark-as-orphan 'first))))
-			       'orphan
+                               (or first-child
+                                   (not (eq mu4e-headers-thread-mark-as-orphan 'first))))
+                               'orphan
                         (if last-child 'last-child
                           (if first-child 'first-child
                             'child)))))))))