diff --git a/src/hb-blob.h b/src/hb-blob.h
index 7f4e3e4fc..74e923d49 100644
--- a/src/hb-blob.h
+++ b/src/hb-blob.h
@@ -39,8 +39,10 @@ HB_BEGIN_DECLS
 /**
  * hb_memory_mode_t:
  * @HB_MEMORY_MODE_DUPLICATE: HarfBuzz immediately makes a copy of the data.
- * @HB_MEMORY_MODE_READONLY: HarfBuzz client will never modify the data
- * @HB_MEMORY_MODE_WRITABLE: HarfBuzz client made a copy of the data solely for HarfBuzz.
+ * @HB_MEMORY_MODE_READONLY: HarfBuzz client will never modify the data,
+ *     and HarfBuzz will never modify the data.
+ * @HB_MEMORY_MODE_WRITABLE: HarfBuzz client made a copy of the data solely
+ *     for HarfBuzz, so HarfBuzz may modify the data.
  * @HB_MEMORY_MODE_READONLY_MAY_MAKE_WRITABLE: See above
  *
  * Data type holding the memory modes available to