diff --git a/lib/notmuch.h b/lib/notmuch.h
index 02604c56..68896ae7 100644
--- a/lib/notmuch.h
+++ b/lib/notmuch.h
@@ -802,6 +802,8 @@ notmuch_query_destroy (notmuch_query_t *query);
  * valid object. Whereas when this function returns FALSE,
  * notmuch_threads_get will return NULL.
  *
+ * If passed a NULL pointer, this function returns FALSE
+ *
  * See the documentation of notmuch_query_search_threads for example
  * code showing how to iterate over a notmuch_threads_t object.
  */
diff --git a/lib/query.cc b/lib/query.cc
index ec60e2e4..60ff8bd9 100644
--- a/lib/query.cc
+++ b/lib/query.cc
@@ -462,6 +462,9 @@ notmuch_threads_valid (notmuch_threads_t *threads)
 {
     unsigned int doc_id;
 
+    if (! threads)
+	return FALSE;
+
     while (threads->doc_id_pos < threads->doc_ids->len) {
 	doc_id = g_array_index (threads->doc_ids, unsigned int,
 				threads->doc_id_pos);