diff --git a/backend/mpc-system/services/account/adapters/input/http/account_handler.go b/backend/mpc-system/services/account/adapters/input/http/account_handler.go
index 3de31549..3271b66f 100644
--- a/backend/mpc-system/services/account/adapters/input/http/account_handler.go
+++ b/backend/mpc-system/services/account/adapters/input/http/account_handler.go
@@ -778,11 +778,12 @@ func (h *AccountHTTPHandler) CreateSigningSession(c *gin.Context) {
 	// Use the selected delegate for signing (not necessarily the account's delegate)
 	delegateShare = selectedDelegateShare
 
-	// Validate we have enough parties
-	if len(partyIDs) < accountOutput.Account.ThresholdT {
+	// Validate we have enough parties (T+1 required for TSS signing)
+	requiredSigners := accountOutput.Account.ThresholdT + 1
+	if len(partyIDs) < requiredSigners {
 		c.JSON(http.StatusBadRequest, gin.H{
 			"error":    "insufficient parties for signing",
-			"required": accountOutput.Account.ThresholdT,
+			"required": requiredSigners,
 			"selected": len(partyIDs),
 		})
 		return
diff --git a/backend/mpc-system/services/account/domain/entities/account.go b/backend/mpc-system/services/account/domain/entities/account.go
index a717a809..1c6950f3 100644
--- a/backend/mpc-system/services/account/domain/entities/account.go
+++ b/backend/mpc-system/services/account/domain/entities/account.go
@@ -140,9 +140,11 @@ func (a *Account) Validate() error {
 }
 
 // SetSigningParties sets the designated signing parties for this account
-// partyIDs must contain exactly ThresholdT parties
+// partyIDs must contain exactly ThresholdT + 1 parties (required signers for TSS)
+// For 2-of-3: ThresholdT=1, so T+1=2 signers required
 func (a *Account) SetSigningParties(partyIDs []string) error {
-	if len(partyIDs) != a.ThresholdT {
+	requiredSigners := a.ThresholdT + 1
+	if len(partyIDs) != requiredSigners {
 		return ErrInvalidSigningPartiesCount
 	}
 	// Check for duplicates
@@ -197,7 +199,7 @@ var (
 	ErrAccountNotFound             = &AccountError{Code: "ACCOUNT_NOT_FOUND", Message: "account not found"}
 	ErrDuplicateUsername           = &AccountError{Code: "DUPLICATE_USERNAME", Message: "username already exists"}
 	ErrDuplicateEmail              = &AccountError{Code: "DUPLICATE_EMAIL", Message: "email already exists"}
-	ErrInvalidSigningPartiesCount  = &AccountError{Code: "INVALID_SIGNING_PARTIES_COUNT", Message: "signing parties count must equal threshold T"}
+	ErrInvalidSigningPartiesCount  = &AccountError{Code: "INVALID_SIGNING_PARTIES_COUNT", Message: "signing parties count must equal threshold T + 1 (required signers)"}
 	ErrInvalidPartyID              = &AccountError{Code: "INVALID_PARTY_ID", Message: "party ID cannot be empty"}
 	ErrDuplicatePartyID            = &AccountError{Code: "DUPLICATE_PARTY_ID", Message: "duplicate party ID in signing parties"}
 )