diff --git a/backend/mpc-system/services/service-party-app/tss-party/main.go b/backend/mpc-system/services/service-party-app/tss-party/main.go
index a03618b7..287fb233 100644
--- a/backend/mpc-system/services/service-party-app/tss-party/main.go
+++ b/backend/mpc-system/services/service-party-app/tss-party/main.go
@@ -595,12 +595,17 @@ func executeSign(
 	sortedPartyIDs := tss.SortPartyIDs(tssPartyIDs)
 
 	// Create peer context and parameters
-	// For co-managed signing: user says "3-of-5" meaning 3 signers needed
-	// tss-lib threshold parameter t means t+1 signers required
-	// So we pass thresholdT-1 to get the correct number of signers
-	// Example: user wants 3 signers -> pass threshold=2 -> tss-lib needs 2+1=3 signers
+	// For signing, the first parameter to NewParameters must be the number of parties
+	// actually participating in the signing (len(sortedPartyIDs)), NOT the original keygen N.
+	// The threshold parameter is the minimum signers minus 1 (tss-lib convention: t means t+1 required)
+	//
+	// For co-managed signing with 3-of-5:
+	// - thresholdN = 5 (original keygen parties) - NOT used here
+	// - thresholdT = 3 (signers needed)
+	// - len(sortedPartyIDs) = 3 (actual signing participants)
+	// - threshold param = thresholdT - 1 = 2 (tss-lib needs 2+1=3 signers)
 	peerCtx := tss.NewPeerContext(sortedPartyIDs)
-	params := tss.NewParameters(tss.S256(), peerCtx, selfTSSID, thresholdN, thresholdT-1)
+	params := tss.NewParameters(tss.S256(), peerCtx, selfTSSID, len(sortedPartyIDs), thresholdT-1)
 
 	// Create channels
 	outCh := make(chan tss.Message, thresholdT*10)