diff --git a/poc/prg.py b/poc/prg.py
index 219f44eb..e760ddf0 100644
--- a/poc/prg.py
+++ b/poc/prg.py
@@ -104,8 +104,8 @@ class PrgSha3(Prg):
     test_vec_name = 'PrgSha3'
 
     def __init__(self, seed, dst, binder):
-        # `dst` is used for domain separation; `seed || binder` is
-        # used as the main input string.
+        # The input is composed of `dst`, the domain separation tag, the
+        # `seed`, and the `binder` string.
         self.shake = SHAKE128.new()
         dst_length = to_le_bytes(len(dst), 1)  # one byte value
         self.shake.update(dst_length)