diff --git a/src/hb-ot-shape-complex-arabic.cc b/src/hb-ot-shape-complex-arabic.cc
index 2cdd7ba8a..0e011e252 100644
--- a/src/hb-ot-shape-complex-arabic.cc
+++ b/src/hb-ot-shape-complex-arabic.cc
@@ -599,7 +599,7 @@ postprocess_glyphs_arabic (const hb_ot_shape_plan_t *plan,
   HB_BUFFER_DEALLOCATE_VAR (buffer, arabic_shaping_action);
 }
 
-/* https://unicode.org/reports/tr53/tr53-1.pdf */
+/* http://www.unicode.org/reports/tr53/ */
 
 static hb_codepoint_t
 modifier_combining_marks[] =