diff --git a/src/main.cpp b/src/main.cpp
index e8fb26de8..8ed811c1a 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -515,10 +515,14 @@ bool IsStandardTx(const CTransaction& tx, string& reason)
 
     BOOST_FOREACH(const CTxIn& txin, tx.vin)
     {
-        // Biggest 'standard' txin is a 3-signature 3-of-3 CHECKMULTISIG
-        // pay-to-script-hash, which is 3 ~80-byte signatures, 3
-        // ~65-byte public keys, plus a few script ops.
-        if (txin.scriptSig.size() > 500) {
+        // Biggest 'standard' txin is a 15-of-15 P2SH multisig with compressed
+        // keys. (remember the 520 byte limit on redeemScript size) That works
+        // out to a (15*(33+1))+3=513 byte redeemScript, 513+1+15*(73+1)=1624
+        // bytes of scriptSig, which we round off to 1650 bytes for some minor
+        // future-proofing. That's also enough to spend a 20-of-20
+        // CHECKMULTISIG scriptPubKey, though such a scriptPubKey is not
+        // considered standard)
+        if (txin.scriptSig.size() > 1650) {
             reason = "scriptsig-size";
             return false;
         }