diff --git a/ThirdParty/custom-opm-flowdiag-app/opm-flowdiagnostics-applications/opm/utility/ECLFluxCalc.cpp b/ThirdParty/custom-opm-flowdiag-app/opm-flowdiagnostics-applications/opm/utility/ECLFluxCalc.cpp
index c4f9429d4f..b3abc0fe15 100644
--- a/ThirdParty/custom-opm-flowdiag-app/opm-flowdiagnostics-applications/opm/utility/ECLFluxCalc.cpp
+++ b/ThirdParty/custom-opm-flowdiag-app/opm-flowdiagnostics-applications/opm/utility/ECLFluxCalc.cpp
@@ -208,6 +208,11 @@ namespace Opm
     ECLFluxCalc::flux(const ECLRestartData& rstrt,
                       const ECLPhaseIndex   phase) const
     {
+        if (! this->phaseIsActive(phase)) {
+            // Inactive phase.  Return empty flux vector.
+            return {};
+        }
+
         // Obtain dynamic data.
         const auto dyn_data = this->phaseProperties(rstrt, phase);
 
@@ -225,6 +230,11 @@ namespace Opm
     ECLFluxCalc::massflux(const ECLRestartData& rstrt,
                           const ECLPhaseIndex   phase) const
     {
+        if (! this->phaseIsActive(phase)) {
+            // Inactive phase.  Return empty (mass) flux vector.
+            return {};
+        }
+
         // Obtain dynamic data.
         const auto dyn_data = this->phaseProperties(rstrt, phase);
 
@@ -297,6 +307,19 @@ namespace Opm
     }
 
 
+    bool ECLFluxCalc::phaseIsActive(const ECLPhaseIndex phase) const
+    {
+        switch (phase) {
+        case ECLPhaseIndex::Aqua:   return this->pvtWat_ != nullptr;
+        case ECLPhaseIndex::Liquid: return this->pvtOil_ != nullptr;
+        case ECLPhaseIndex::Vapour: return this->pvtGas_ != nullptr;
+        }
+
+        throw std::invalid_argument {
+            "phaseIsActive(): Invalid Phase Identifier"
+        };
+    }
+
 
     ECLFluxCalc::DynamicData
     ECLFluxCalc::phaseProperties(const ECLRestartData& rstrt,
diff --git a/ThirdParty/custom-opm-flowdiag-app/opm-flowdiagnostics-applications/opm/utility/ECLFluxCalc.hpp b/ThirdParty/custom-opm-flowdiag-app/opm-flowdiagnostics-applications/opm/utility/ECLFluxCalc.hpp
index 341f91326a..f12fd9d9d6 100644
--- a/ThirdParty/custom-opm-flowdiag-app/opm-flowdiagnostics-applications/opm/utility/ECLFluxCalc.hpp
+++ b/ThirdParty/custom-opm-flowdiag-app/opm-flowdiagnostics-applications/opm/utility/ECLFluxCalc.hpp
@@ -131,6 +131,8 @@ namespace Opm
                               const DynamicData& dyn_data) const;
 
 
+        bool phaseIsActive(const ECLPhaseIndex phase) const;
+
         DynamicData gasPVT(const ECLRestartData& rstrt,
                            DynamicData&&         dyn_data) const;