diff --git a/opm/core/props/BlackoilPhases.hpp b/opm/core/props/BlackoilPhases.hpp
index c4514555a..1cbb3afa4 100644
--- a/opm/core/props/BlackoilPhases.hpp
+++ b/opm/core/props/BlackoilPhases.hpp
@@ -20,6 +20,7 @@
 #ifndef OPM_BLACKOILPHASES_HEADER_INCLUDED
 #define OPM_BLACKOILPHASES_HEADER_INCLUDED
 
+#include <array>
 
 namespace Opm
 {
@@ -42,9 +43,10 @@ namespace Opm
 
     struct PhaseUsage : public BlackoilPhases
     {
+        std::array<int, MaxNumPhases + NumCryptoPhases> phase_used;
+        std::array<int, MaxNumPhases + NumCryptoPhases> phase_pos;
+
         int num_phases;
-        int phase_used[MaxNumPhases + NumCryptoPhases];
-        int phase_pos[MaxNumPhases + NumCryptoPhases];
         bool has_solvent;
         bool has_polymer;
         bool has_energy;
diff --git a/opm/core/props/phaseUsageFromDeck.hpp b/opm/core/props/phaseUsageFromDeck.hpp
index 3d0277f98..873410031 100644
--- a/opm/core/props/phaseUsageFromDeck.hpp
+++ b/opm/core/props/phaseUsageFromDeck.hpp
@@ -34,7 +34,7 @@ namespace Opm
     /// Determine the active phases
     inline PhaseUsage phaseUsage(const Phases& phases) {
         PhaseUsage pu;
-        std::fill(pu.phase_used, pu.phase_used + BlackoilPhases::MaxNumPhases + BlackoilPhases::NumCryptoPhases, 0);
+        pu.phase_used.fill(0);
 
         // Discover phase usage.
         pu.phase_used[BlackoilPhases::Aqua] = phases.active(Phase::WATER);