diff --git a/src/hb-font.cc b/src/hb-font.cc
index f2127c2b1..da5162b98 100644
--- a/src/hb-font.cc
+++ b/src/hb-font.cc
@@ -1343,6 +1343,9 @@ hb_font_get_glyph_contour_point (hb_font_t      *font,
  *
  * Fetches the glyph-name string for a glyph ID in the specified @font.
  *
+ * According to the OpenType specification, glyph names are limited to 63
+ * characters and can only contain (a subset of) ASCII.
+ *
  * Return value: `true` if data found, `false` otherwise
  *
  * Since: 0.9.2