diff --git a/backend/mpc-system/services/server-party/adapters/output/grpc/message_router_client.go b/backend/mpc-system/services/server-party/adapters/output/grpc/message_router_client.go
index d69c3f4e..4104ccbc 100644
--- a/backend/mpc-system/services/server-party/adapters/output/grpc/message_router_client.go
+++ b/backend/mpc-system/services/server-party/adapters/output/grpc/message_router_client.go
@@ -637,16 +637,28 @@ func (c *MessageRouterClient) JoinSession(
 		}
 
 		// Convert response to SessionInfo
-		participants := make([]use_cases.ParticipantInfo, len(resp.OtherParties))
-		for i, p := range resp.OtherParties {
+		// Include both other parties AND self in the participants list
+		participants := make([]use_cases.ParticipantInfo, 0, len(resp.OtherParties)+1)
+
+		// Add self first
+		participants = append(participants, use_cases.ParticipantInfo{
+			PartyID:    partyID,
+			PartyIndex: int(resp.PartyIndex),
+		})
+		logger.Debug("Added self to participants",
+			zap.String("party_id", partyID),
+			zap.Int32("party_index", resp.PartyIndex))
+
+		// Add other parties
+		for _, p := range resp.OtherParties {
 			logger.Debug("Received party_index from Message Router",
 				zap.String("party_id", p.PartyId),
 				zap.Int32("party_index", p.PartyIndex))
 
-			participants[i] = use_cases.ParticipantInfo{
+			participants = append(participants, use_cases.ParticipantInfo{
 				PartyID:    p.PartyId,
 				PartyIndex: int(p.PartyIndex),
-			}
+			})
 		}
 
 		sessionInfo := &use_cases.SessionInfo{