diff --git a/lib/thread.cc b/lib/thread.cc
index 46a50e80..60e9a666 100644
--- a/lib/thread.cc
+++ b/lib/thread.cc
@@ -25,7 +25,8 @@
 #include <glib.h>                                       /* GHashTable */
 
 #ifdef DEBUG_THREADING
-#define THREAD_DEBUG(format, ...) fprintf (stderr, format " (%s).\n", ##__VA_ARGS__, __location__)
+#define THREAD_DEBUG(format, ...) fprintf (stderr, "DT: " format " (%s).\n", ##__VA_ARGS__, \
+					   __location__)
 #else
 #define THREAD_DEBUG(format, ...) do {} while (0)       /* ignored */
 #endif
@@ -400,7 +401,7 @@ _parent_via_in_reply_to (notmuch_thread_t *thread, notmuch_message_t *message)
     const char *in_reply_to;
 
     in_reply_to = _notmuch_message_get_in_reply_to (message);
-    THREAD_DEBUG ("checking message = %s in_reply_to=%s\n",
+    THREAD_DEBUG ("checking message = %s in_reply_to=%s",
 		  notmuch_message_get_message_id (message), in_reply_to);
 
     if (in_reply_to && (! EMPTY_STRING (in_reply_to)) &&
@@ -423,31 +424,31 @@ _parent_or_toplevel (notmuch_thread_t *thread, notmuch_message_t *message)
     const notmuch_string_list_t *references =
 	_notmuch_message_get_references (message);
 
-    THREAD_DEBUG ("trying to reparent via references: %s\n",
+    THREAD_DEBUG ("trying to reparent via references: %s",
 		  notmuch_message_get_message_id (message));
 
     for (notmuch_string_node_t *ref_node = references->head;
 	 ref_node; ref_node = ref_node->next) {
-	THREAD_DEBUG ("checking reference=%s\n", ref_node->string);
+	THREAD_DEBUG ("checking reference=%s", ref_node->string);
 	if ((g_hash_table_lookup_extended (thread->message_hash,
 					   ref_node->string, NULL,
 					   (void **) &new_parent))) {
 	    size_t new_depth = _notmuch_message_get_thread_depth (new_parent);
-	    THREAD_DEBUG ("got depth %lu\n", new_depth);
+	    THREAD_DEBUG ("got depth %lu", new_depth);
 	    if (new_depth > max_depth || ! parent) {
-		THREAD_DEBUG ("adding at depth %lu parent=%s\n", new_depth, ref_node->string);
+		THREAD_DEBUG ("adding at depth %lu parent=%s", new_depth, ref_node->string);
 		max_depth = new_depth;
 		parent = new_parent;
 	    }
 	}
     }
     if (parent) {
-	THREAD_DEBUG ("adding reply %s to parent=%s\n",
+	THREAD_DEBUG ("adding reply %s to parent=%s",
 		      notmuch_message_get_message_id (message),
 		      notmuch_message_get_message_id (parent));
 	_notmuch_message_add_reply (parent, message);
     } else {
-	THREAD_DEBUG ("adding as toplevel %s\n",
+	THREAD_DEBUG ("adding as toplevel %s",
 		      notmuch_message_get_message_id (message));
 	_notmuch_message_list_add_message (thread->toplevel_list, message);
     }
@@ -482,13 +483,13 @@ _resolve_thread_relationships (notmuch_thread_t *thread)
      */
     if (first_node) {
 	message = first_node->message;
-	THREAD_DEBUG ("checking first message  %s\n",
+	THREAD_DEBUG ("checking first message  %s",
 		      notmuch_message_get_message_id (message));
 
 	if (_notmuch_message_list_empty (maybe_toplevel_list) ||
 	    ! _parent_via_in_reply_to (thread, message)) {
 
-	    THREAD_DEBUG ("adding first message as toplevel = %s\n",
+	    THREAD_DEBUG ("adding first message as toplevel = %s",
 			  notmuch_message_get_message_id (message));
 	    _notmuch_message_list_add_message (maybe_toplevel_list, message);
 	}