diff --git a/ProcessLib/HydroMechanics/CreateHydroMechanicsProcess.cpp b/ProcessLib/HydroMechanics/CreateHydroMechanicsProcess.cpp
index b3b09939772da87a9b944ddc28767bbdd8bbb36b..a3d8e4a949a17128861411e88f4d28bc09c0164c 100644
--- a/ProcessLib/HydroMechanics/CreateHydroMechanicsProcess.cpp
+++ b/ProcessLib/HydroMechanics/CreateHydroMechanicsProcess.cpp
@@ -183,7 +183,8 @@ std::unique_ptr<Process> createHydroMechanicsProcess(
     // Reference temperature
     const auto& reference_temperature =
         //! \ogs_file_param{prj__processes__process__HYDRO_MECHANICS__reference_temperature}
-        config.getConfigParameterOptional<double>("reference_temperature");
+        config.getConfigParameter<double>(
+            "reference_temperature", std::numeric_limits<double>::quiet_NaN());
 
     HydroMechanicsProcessData<DisplacementDim> process_data{
         std::move(material),
@@ -195,7 +196,7 @@ std::unique_ptr<Process> createHydroMechanicsProcess(
         porosity,
         solid_density,
         specific_body_force,
-        *reference_temperature};
+        reference_temperature};
 
     SecondaryVariableCollection secondary_variables;
 
diff --git a/ProcessLib/LIE/HydroMechanics/CreateHydroMechanicsProcess.cpp b/ProcessLib/LIE/HydroMechanics/CreateHydroMechanicsProcess.cpp
index 5c8ffbddd283e2731cf20e9bc7e03f5257b0008c..bac9e7073808a4c1fe941ecb828ecefd75b3610c 100644
--- a/ProcessLib/LIE/HydroMechanics/CreateHydroMechanicsProcess.cpp
+++ b/ProcessLib/LIE/HydroMechanics/CreateHydroMechanicsProcess.cpp
@@ -305,7 +305,8 @@ std::unique_ptr<Process> createHydroMechanicsProcess(
     // Reference temperature
     const auto& reference_temperature =
         //! \ogs_file_param{prj__processes__process__HYDRO_MECHANICS_WITH_LIE__reference_temperature}
-        config.getConfigParameterOptional<double>("reference_temperature");
+        config.getConfigParameter<double>(
+            "reference_temperature", std::numeric_limits<double>::quiet_NaN());
 
     HydroMechanicsProcessData<GlobalDim> process_data{
         std::move(material),
@@ -322,7 +323,7 @@ std::unique_ptr<Process> createHydroMechanicsProcess(
         initial_effective_stress,
         initial_fracture_effective_stress,
         deactivate_matrix_in_flow,
-        *reference_temperature};
+        reference_temperature};
 
     SecondaryVariableCollection secondary_variables;
 
diff --git a/ProcessLib/LIE/SmallDeformation/CreateSmallDeformationProcess.cpp b/ProcessLib/LIE/SmallDeformation/CreateSmallDeformationProcess.cpp
index 33513e74088ed6f33d884da474598ce5f278f8a4..edcac74b40af1743435018ad89a835b2e3b6c011 100644
--- a/ProcessLib/LIE/SmallDeformation/CreateSmallDeformationProcess.cpp
+++ b/ProcessLib/LIE/SmallDeformation/CreateSmallDeformationProcess.cpp
@@ -170,11 +170,12 @@ std::unique_ptr<Process> createSmallDeformationProcess(
     // Reference temperature
     const auto& reference_temperature =
         //! \ogs_file_param{prj__processes__process__SMALL_DEFORMATION_WITH_LIE__reference_temperature}
-        config.getConfigParameterOptional<double>("reference_temperature");
+        config.getConfigParameter<double>(
+            "reference_temperature", std::numeric_limits<double>::quiet_NaN());
 
     SmallDeformationProcessData<DisplacementDim> process_data(
         std::move(material), std::move(fracture_model),
-        std::move(vec_fracture_property), *reference_temperature);
+        std::move(vec_fracture_property), reference_temperature);
 
     SecondaryVariableCollection secondary_variables;
 
diff --git a/ProcessLib/SmallDeformation/CreateSmallDeformationProcess.cpp b/ProcessLib/SmallDeformation/CreateSmallDeformationProcess.cpp
index 44af30c54106f004e3b66873dac52c3e2f895f41..15dee6ba84edde6ff6aef94d3d86c00007f46abd 100644
--- a/ProcessLib/SmallDeformation/CreateSmallDeformationProcess.cpp
+++ b/ProcessLib/SmallDeformation/CreateSmallDeformationProcess.cpp
@@ -96,11 +96,12 @@ createSmallDeformationProcess(
     // Reference temperature
     const auto& reference_temperature =
         //! \ogs_file_param{prj__processes__process__SMALL_DEFORMATION__reference_temperature}
-        config.getConfigParameterOptional<double>("reference_temperature");
+        config.getConfigParameter<double>(
+            "reference_temperature", std::numeric_limits<double>::quiet_NaN());
 
     SmallDeformationProcessData<DisplacementDim> process_data{
         std::move(material), solid_density, specific_body_force,
-        *reference_temperature};
+        reference_temperature};
 
     SecondaryVariableCollection secondary_variables;