diff --git a/cmd/clientsim/main.go b/cmd/clientsim/main.go
index 0ee818f..f64236f 100644
--- a/cmd/clientsim/main.go
+++ b/cmd/clientsim/main.go
@@ -322,6 +322,13 @@ func (c *ClientHandler) ResponseData(ctx context.Context, in <-chan []byte, resp
 				return fmt.Errorf("could not unmarshal fetch CRL response data: %w", err)
 			}
 
+			response.Response = &resp
+		case messages.RespSignCertificate:
+			var resp messages.SignCertificateResponse
+			if err := msgpack.Unmarshal(frame, &resp); err != nil {
+				return fmt.Errorf("could not unmarshal sign certificate response data: %w", err)
+			}
+
 			response.Response = &resp
 		default:
 			return fmt.Errorf("unhandled response code %s", response.Announce.Code)