diff --git a/ProcessLib/HeatTransportBHE/BHE/BHE_1U.cpp b/ProcessLib/HeatTransportBHE/BHE/BHE_1U.cpp
index 4a6272803f63b23b09dc726e9596346d7645cf1f..2ef82cbe6b649f3039adc7a35e9d1c90d51b5ab8 100644
--- a/ProcessLib/HeatTransportBHE/BHE/BHE_1U.cpp
+++ b/ProcessLib/HeatTransportBHE/BHE/BHE_1U.cpp
@@ -124,8 +124,9 @@ double compute_R_gg(double const chi, double const R_gs, double const R_ar,
 /// Check if constraints regarding negative thermal resistances are violated
 /// apply correction procedure.
 /// Section (1.5.5) in FEFLOW White Papers Vol V.
-std::tuple<double, double, double> thermalResistancesGroutSoil(
-    double const chi, double const R_ar, double const R_g)
+std::array<double, 3> thermalResistancesGroutSoil(double const chi,
+                                                  double const R_ar,
+                                                  double const R_g)
 {
     double R_gs = compute_R_gs(chi, R_g);
     double R_gg =
diff --git a/ProcessLib/HeatTransportBHE/BHE/BHE_2U.cpp b/ProcessLib/HeatTransportBHE/BHE/BHE_2U.cpp
index 0fbc897fb0ee9b151415319da2335589c3993317..99555a2ea541cb02815d5efbc62664e8c1db6ba5 100644
--- a/ProcessLib/HeatTransportBHE/BHE/BHE_2U.cpp
+++ b/ProcessLib/HeatTransportBHE/BHE/BHE_2U.cpp
@@ -142,11 +142,10 @@ double compute_R_gg_2U(double const chi, double const R_gs, double const R_ar,
 /// Check if constraints regarding negative thermal resistances are violated
 /// apply correction procedure.
 /// Section (1.5.5) in FEFLOW White Papers Vol V.
-std::tuple<double, double, double, double> thermalResistancesGroutSoil2U(
-    double const chi,
-    double const R_ar_1,
-    double const R_ar_2,
-    double const R_g)
+std::array<double, 4> thermalResistancesGroutSoil2U(double const chi,
+                                                    double const R_ar_1,
+                                                    double const R_ar_2,
+                                                    double const R_g)
 {
     double R_gs = compute_R_gs_2U(chi, R_g);
     double R_gg_1 = compute_R_gg_2U(chi, R_gs, R_ar_1, R_g);