diff --git a/opm/simulators/wells/BlackoilWellModelGeneric.cpp b/opm/simulators/wells/BlackoilWellModelGeneric.cpp
index 86be56640..8858d3d6a 100644
--- a/opm/simulators/wells/BlackoilWellModelGeneric.cpp
+++ b/opm/simulators/wells/BlackoilWellModelGeneric.cpp
@@ -350,14 +350,13 @@ initializeWellPerfData()
                         hasFirstConnection = true;
                     }
 
-                    auto pd = PerforationData{};
+                    auto& pd = well_perf_data_[well_index].emplace_back();
+
                     pd.cell_index = active_index;
                     pd.connection_transmissibility_factor = connection.CF();
                     pd.satnum_id = connection.satTableId();
                     pd.ecl_index = connection_index;
 
-                    well_perf_data_[well_index].push_back(pd);
-
                     parallelWellInfo.pushBackEclIndex(connection_index_above,
                                                       connection_index);
                 }
diff --git a/opm/simulators/wells/ParallelPAvgDynamicSourceData.cpp b/opm/simulators/wells/ParallelPAvgDynamicSourceData.cpp
index 1edf6da91..50da7086b 100644
--- a/opm/simulators/wells/ParallelPAvgDynamicSourceData.cpp
+++ b/opm/simulators/wells/ParallelPAvgDynamicSourceData.cpp
@@ -148,7 +148,19 @@ void Opm::ParallelPAvgDynamicSourceData::defineCommunication()
 
     // 4) Build translation mapping from source term element indices to
     //    storage indices.
-    this->storageIndex_.resize(allIndices.size());
+    //
+    //    Note that if the source terms aren't all active--e.g., if a well
+    //    is connected in deactivated cells--then allIndices is not a
+    //    permutation of 0..allIndices.size()-1 and the maximum source
+    //    location may exceed size()-1.  Resize the storageIndex_ according
+    //    to the largest source location ID.
+    if (auto maxIxPos = std::max_element(allIndices.begin(), allIndices.end());
+        maxIxPos != allIndices.end())
+    {
+        // +1 for zero-based indices.
+        this->storageIndex_.resize(*maxIxPos + 1);
+    }
+
     auto storageIx = std::vector<double>::size_type{0};
     for (const auto& elemIndex : allIndices) {
         this->storageIndex_[elemIndex] = storageIx++;
diff --git a/opm/simulators/wells/PerforationData.hpp b/opm/simulators/wells/PerforationData.hpp
index a9ddeab9d..f195746cf 100644
--- a/opm/simulators/wells/PerforationData.hpp
+++ b/opm/simulators/wells/PerforationData.hpp
@@ -28,12 +28,12 @@ namespace Opm
 /// Static data associated with a well perforation.
 struct PerforationData
 {
-    int cell_index;
-    double connection_transmissibility_factor;
-    double connection_d_factor;
-    int satnum_id;
+    int cell_index{};
+    double connection_transmissibility_factor{};
+    double connection_d_factor{};
+    int satnum_id{};
     /// \brief The original index of the perforation in ECL Schedule
-    std::size_t ecl_index;
+    std::size_t ecl_index{};
 };
 
 struct PerforationRates