diff --git a/include/CoolPropFluid.h b/include/CoolPropFluid.h
index d247a6ec..04505fe2 100644
--- a/include/CoolPropFluid.h
+++ b/include/CoolPropFluid.h
@@ -293,6 +293,8 @@ public:
                 BibTeX_conductivity;  ///< The BibTeX key for the conductivity model
     bool viscosity_using_ECS; ///< A flag for whether to use extended corresponding states for viscosity.  False for no
     bool conductivity_using_ECS; ///< A flag for whether to use extended corresponding states for conductivity.  False for no
+	bool conductivity_model_provided; ///< A flag for whether thermal conductivity model is provided.  False for no
+	bool viscosity_model_provided; ///< A flag for whether viscosity model is provided.  False for no
     long double sigma_eta, ///< The Lennard-Jones 12-6 \f$ \sigma \f$ parameter
                 epsilon_over_k; ///< The Lennard-Jones 12-6 \f$ \varepsilon/k \f$ parameter
     ViscosityHardcodedEnum hardcoded_viscosity; ///< Hardcoded flags for the viscosity
@@ -301,6 +303,8 @@ public:
                             hardcoded_conductivity = CONDUCTIVITY_NOT_HARDCODED;
                             viscosity_using_ECS = false;
                             conductivity_using_ECS = false;
+							viscosity_model_provided = false;
+							conductivity_model_provided = false;
     };
 };
 
diff --git a/src/Backends/Helmholtz/Fluids/FluidLibrary.h b/src/Backends/Helmholtz/Fluids/FluidLibrary.h
index 2b8a2ef9..cef386f7 100644
--- a/src/Backends/Helmholtz/Fluids/FluidLibrary.h
+++ b/src/Backends/Helmholtz/Fluids/FluidLibrary.h
@@ -856,11 +856,13 @@ protected:
         // Parse viscosity
         if (transport.HasMember("viscosity")){
             parse_viscosity(transport["viscosity"],fluid);
+			fluid.transport.viscosity_model_provided = true;
         }
 
         // Parse thermal conductivity
         if (transport.HasMember("conductivity")){
             parse_thermal_conductivity(transport["conductivity"],fluid);
+			fluid.transport.conductivity_model_provided = true;
         }
     };
 
diff --git a/src/Backends/Helmholtz/HelmholtzEOSMixtureBackend.cpp b/src/Backends/Helmholtz/HelmholtzEOSMixtureBackend.cpp
index 2d42d1ba..9722f1c9 100644
--- a/src/Backends/Helmholtz/HelmholtzEOSMixtureBackend.cpp
+++ b/src/Backends/Helmholtz/HelmholtzEOSMixtureBackend.cpp
@@ -399,6 +399,10 @@ long double HelmholtzEOSMixtureBackend::calc_viscosity(void)
     {
         // Get a reference for code cleanness
         CoolPropFluid &component = *(components[0]);
+		
+		if (!component.transport.viscosity_model_provided){
+			throw ValueError(format("Viscosity model is not available for this fluid"));
+		}
 
         // Check if using ECS
         if (component.transport.viscosity_using_ECS)
@@ -465,6 +469,10 @@ long double HelmholtzEOSMixtureBackend::calc_conductivity(void)
     {
         // Get a reference for code cleanness
         CoolPropFluid &component = *(components[0]);
+		
+		if (!component.transport.conductivity_model_provided){
+			throw ValueError(format("Thermal conductivity model is not available for this fluid"));
+		}
 
         // Check if using ECS
         if (component.transport.conductivity_using_ECS)