diff --git a/src/dft/dft.c b/src/dft/dft.c
index 6132e28..9302a38 100644
--- a/src/dft/dft.c
+++ b/src/dft/dft.c
@@ -45,6 +45,7 @@ static bool initialize_freetype()
     return true;
 }
 
+/* outline_size is in 64ths of a pixel. */
 dft_glyph_t * dft_glyph_new(dft_font_t * dft_font, uint32_t char_code, int32_t outline_size)
 {
     FT_Glyph glyph;