diff --git a/plugins/trustedcoin/trustedcoin.py b/plugins/trustedcoin/trustedcoin.py
index 6c4cfdfd1..0dab526aa 100644
--- a/plugins/trustedcoin/trustedcoin.py
+++ b/plugins/trustedcoin/trustedcoin.py
@@ -418,7 +418,10 @@ class TrustedCoinPlugin(BasePlugin):
         words = seed.split()
         n = len(words)
         # old version use long seed phrases
-        if n >= 24:
+        if n >= 20:
+            # note: pre-2.7 2fa seeds were typically 24-25 words, however they
+            # could probabilistically be arbitrarily shorter due to a bug. (see #3611)
+            # the probability of it being < 20 words is about 2^(-(256+12-19*11)) = 2^(-59)
             assert passphrase == ''
             xprv1, xpub1 = self.get_xkeys(' '.join(words[0:12]), '', "m/")
             xprv2, xpub2 = self.get_xkeys(' '.join(words[12:]), '', "m/")