diff --git a/include/gnss_utils/tdcp.h b/include/gnss_utils/tdcp.h
index a543441d7c23fb1aba41b9303072c6ebffc50692..eb323991041bd191b3828f4631a428a72d43a4fe 100644
--- a/include/gnss_utils/tdcp.h
+++ b/include/gnss_utils/tdcp.h
@@ -66,9 +66,9 @@ TdcpOutput Tdcp(SnapshotPtr               snapshot_r,
 TdcpOutput Tdcp(const Eigen::Vector3d&  x_r,
                 Eigen::MatrixXd&        A,
                 Eigen::VectorXd&        r,
-                Eigen::VectorXd&        drho_m,
-                Eigen::MatrixXd&        s_k,
-                Eigen::MatrixXd&        s_r,
+                const Eigen::VectorXd&  drho_m,
+                const Eigen::MatrixXd&  s_k,
+                const Eigen::MatrixXd&  s_r,
                 const Eigen::Vector4d&  d_0,
                 const double&           var_tdcp,
                 std::set<int>&          raim_discarded_rows,
diff --git a/src/tdcp.cpp b/src/tdcp.cpp
index 7f9360477b07bbd520ae370a9e51cdcf483162df..4188a44491d0f794155c301eecfebe15025c8831 100644
--- a/src/tdcp.cpp
+++ b/src/tdcp.cpp
@@ -307,9 +307,9 @@ TdcpOutput Tdcp(SnapshotPtr               snapshot_r,
 TdcpOutput Tdcp(const Eigen::Vector3d&  x_r,
                 Eigen::MatrixXd&        A,
                 Eigen::VectorXd&        r,
-                Eigen::VectorXd&        drho_m,
-                Eigen::MatrixXd&        s_k,
-                Eigen::MatrixXd&        s_r,
+                const Eigen::VectorXd&  drho_m,
+                const Eigen::MatrixXd&  s_k,
+                const Eigen::MatrixXd&  s_r,
                 const Eigen::Vector4d&  d_0,
                 const double&           var_tdcp,
                 std::set<int>&          raim_discarded_rows,
@@ -551,7 +551,7 @@ TdcpOutput Tdcp(const Eigen::Vector3d&  x_r,
                 A.row(worst_sat_row) = Eigen::Vector4d::Zero().transpose();
                 r(worst_sat_row)     = 0;
 
-                // Choose de best RAIM solution
+                // Choose the best RAIM solution
                 d     = best_d;
                 cov_d = (A.transpose() * A).inverse();
                 residual = best_residual;