diff --git a/test/api/test-multithread.c b/test/api/test-multithread.c
index 6881a00fc..898f19a0f 100644
--- a/test/api/test-multithread.c
+++ b/test/api/test-multithread.c
@@ -135,6 +135,7 @@ int
 main (int argc, char **argv)
 {
   // Dummy call to alleviate _guess_segment_properties thread safety-ness
+  // https://github.com/harfbuzz/harfbuzz/issues/1191
   hb_language_get_default ();
 
   hb_blob_t *blob = hb_blob_create_from_file (path);