diff --git a/opm/simulators/wells/GasLiftSingleWell_impl.hpp b/opm/simulators/wells/GasLiftSingleWell_impl.hpp
index 07bd46354..1611f8c43 100644
--- a/opm/simulators/wells/GasLiftSingleWell_impl.hpp
+++ b/opm/simulators/wells/GasLiftSingleWell_impl.hpp
@@ -156,11 +156,7 @@ setupPhaseVariables_()
 {
     const auto& pu = this->phase_usage_;
     bool num_phases_ok = (pu.num_phases == 3);
-    if (pu.num_phases == 2
-        && pu.phase_used[BlackoilPhases::Aqua] == 1
-        && pu.phase_used[BlackoilPhases::Liquid] == 1
-        && pu.phase_used[BlackoilPhases::Vapour] == 0)
-    {
+    if (pu.num_phases == 2) {
         // NOTE: We support two-phase oil-water flow, by setting the gas flow rate
         //   to zero. This is done by initializing the potential vector to zero:
         //
@@ -171,7 +167,16 @@ setupPhaseVariables_()
         //  has been adapted to the two-phase oil-water case, see the comment
         //  in WellInterfaceGeneric.cpp for the method adaptRatesForVFP() for
         //  more information.
-        num_phases_ok = true;  // two-phase oil-water is also supported
+        if (    pu.phase_used[BlackoilPhases::Aqua] == 1
+             && pu.phase_used[BlackoilPhases::Liquid] == 1
+             && pu.phase_used[BlackoilPhases::Vapour] == 0)
+        {
+            num_phases_ok = true;  // two-phase oil-water is also supported
+        }
+        else {
+            throw std::logic_error("Two-phase gas lift optimization only supported"
+                                  " for oil and water");
+        }
     }
     assert(num_phases_ok);
     this->oil_pos_ = pu.phase_pos[Oil];
diff --git a/opm/simulators/wells/WellInterfaceGeneric.cpp b/opm/simulators/wells/WellInterfaceGeneric.cpp
index cad14e6f1..a627b1603 100644
--- a/opm/simulators/wells/WellInterfaceGeneric.cpp
+++ b/opm/simulators/wells/WellInterfaceGeneric.cpp
@@ -109,13 +109,18 @@ WellInterfaceGeneric::WellInterfaceGeneric(const Well& well,
 void WellInterfaceGeneric::adaptRatesForVFP(std::vector<double>& rates) const
 {
     const auto& pu = this->phaseUsage();
-    if (pu.num_phases == 2
-        && pu.phase_used[BlackoilPhases::Aqua] == 1
-        && pu.phase_used[BlackoilPhases::Liquid] == 1
-        && pu.phase_used[BlackoilPhases::Vapour] == 0)
-    {
-        assert(rates.size() == 2);
-        rates.push_back(0.0);  // set gas rate to zero
+    if (pu.num_phases == 2) {
+        if (    pu.phase_used[BlackoilPhases::Aqua] == 1
+             && pu.phase_used[BlackoilPhases::Liquid] == 1
+             && pu.phase_used[BlackoilPhases::Vapour] == 0)
+        {
+            assert(rates.size() == 2);
+            rates.push_back(0.0);  // set gas rate to zero
+        }
+        else {
+            throw std::logic_error("Two-phase VFP calculation only "
+                                   "supported for oil and water");
+        }
     }
 }