diff --git a/backend/mpc-system/services/account/adapters/input/http/co_managed_handler.go b/backend/mpc-system/services/account/adapters/input/http/co_managed_handler.go
index 105f995b..ff89c229 100644
--- a/backend/mpc-system/services/account/adapters/input/http/co_managed_handler.go
+++ b/backend/mpc-system/services/account/adapters/input/http/co_managed_handler.go
@@ -123,19 +123,10 @@ func (h *CoManagedHTTPHandler) CreateSession(c *gin.Context) {
 	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
 	defer cancel()
 
-	// IMPORTANT: Convert user-friendly threshold to tss-lib format
-	// User says "3-of-5" meaning 3 signers needed
-	// tss-lib threshold t means t+1 signers needed
-	// So we store t-1: user's 3 becomes 2, tss-lib needs 2+1=3 signers
-	// This matches persistent-only behavior (see account.go:144)
-	// ROLLBACK: If this breaks, revert this change and the tss-party/main.go changes
-	tssThresholdT := req.ThresholdT - 1
-
 	logger.Info("Creating co-managed keygen session",
 		zap.String("wallet_name", req.WalletName),
 		zap.Int("threshold_n", req.ThresholdN),
-		zap.Int("threshold_t_user", req.ThresholdT),
-		zap.Int("threshold_t_tss", tssThresholdT),
+		zap.Int("threshold_t", req.ThresholdT),
 		zap.Int("persistent_count", persistentCount),
 		zap.Int("external_count", externalCount),
 		zap.String("initiator_party_id", req.InitiatorPartyID))
@@ -145,7 +136,7 @@ func (h *CoManagedHTTPHandler) CreateSession(c *gin.Context) {
 		req.WalletName,
 		inviteCode,
 		int32(req.ThresholdN),
-		int32(tssThresholdT),
+		int32(req.ThresholdT),
 		int32(persistentCount),
 		int32(externalCount),
 		3600, // 1 hour expiry for session creation phase
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 a9f37a9d..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
@@ -597,15 +597,15 @@ func executeSign(
 	// Create peer context and parameters
 	// 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 must match what was used during keygen.
+	// 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 for party count
-	// - thresholdT = 3 (threshold from keygen, meaning 3+1=4 parties needed... but we have 3 signers)
+	// - thresholdN = 5 (original keygen parties) - NOT used here
+	// - thresholdT = 3 (signers needed)
 	// - len(sortedPartyIDs) = 3 (actual signing participants)
-	// - threshold param = thresholdT (must match keygen threshold)
+	// - threshold param = thresholdT - 1 = 2 (tss-lib needs 2+1=3 signers)
 	peerCtx := tss.NewPeerContext(sortedPartyIDs)
-	params := tss.NewParameters(tss.S256(), peerCtx, selfTSSID, len(sortedPartyIDs), thresholdT)
+	params := tss.NewParameters(tss.S256(), peerCtx, selfTSSID, len(sortedPartyIDs), thresholdT-1)
 
 	// Create channels
 	outCh := make(chan tss.Message, thresholdT*10)