diff --git a/opm/simulators/flow/ExtboContainer.cpp b/opm/simulators/flow/ExtboContainer.cpp
index 6f9ee638d..894596322 100644
--- a/opm/simulators/flow/ExtboContainer.cpp
+++ b/opm/simulators/flow/ExtboContainer.cpp
@@ -58,6 +58,14 @@ assignVolumes(const unsigned globalDofIdx,
     Y_volume_[globalDofIdx] = yVolume;
 }
 
+template<class Scalar>
+void ExtboContainer<Scalar>::
+assignZFraction(const unsigned globalDofIdx,
+                const Scalar zFraction)
+{
+    Z_fraction_[globalDofIdx] = zFraction;
+}
+
 template<class Scalar>
 void ExtboContainer<Scalar>::
 outputRestart(data::Solution& sol)
diff --git a/opm/simulators/flow/ExtboContainer.hpp b/opm/simulators/flow/ExtboContainer.hpp
index 802e84334..73044b74c 100644
--- a/opm/simulators/flow/ExtboContainer.hpp
+++ b/opm/simulators/flow/ExtboContainer.hpp
@@ -44,6 +44,9 @@ public:
                        const Scalar xVolume,
                        const Scalar yVolume);
 
+    void assignZFraction(const unsigned globalDofIdx,
+                         const Scalar zFraction);
+
     void outputRestart(data::Solution& sol);
 
     bool allocated() const
diff --git a/opm/simulators/flow/OutputBlackoilModule.hpp b/opm/simulators/flow/OutputBlackoilModule.hpp
index 89f2b726e..39f72aeb2 100644
--- a/opm/simulators/flow/OutputBlackoilModule.hpp
+++ b/opm/simulators/flow/OutputBlackoilModule.hpp
@@ -447,10 +447,8 @@ public:
                 this->extboC_.assignVolumes(globalDofIdx,
                                             intQuants.xVolume().value(),
                                             intQuants.yVolume().value());
-            }
-
-            if (!this->extboC_.Z_fraction_.empty()) {
-                this->extboC_.Z_fraction_[globalDofIdx] = intQuants.zFraction().value();
+                this->extboC_.assignZFraction(globalDofIdx,
+                                              intQuants.zFraction().value());
             }
 
             if (!this->extboC_.mFracCo2_.empty()) {