diff --git a/opm/simulators/utils/MPIPacker.cpp b/opm/simulators/utils/MPIPacker.cpp
index cf25f7a4c..430a10b26 100644
--- a/opm/simulators/utils/MPIPacker.cpp
+++ b/opm/simulators/utils/MPIPacker.cpp
@@ -70,7 +70,7 @@ packSize(const std::string& data, Parallel::MPIComm comm)
     MPI_Pack_size(1, Dune::MPITraits<std::size_t>::getType(), comm, &size);
     int totalSize = size;
     MPI_Pack_size(data.size(), MPI_CHAR, comm, &size);
-    return static_cast<std::size_t>(totalSize + size);
+    return totalSize + size;
 }
 
 void Packing<false,std::string>::
diff --git a/opm/simulators/utils/MPIPacker.hpp b/opm/simulators/utils/MPIPacker.hpp
index 8263d1645..cd4406280 100644
--- a/opm/simulators/utils/MPIPacker.hpp
+++ b/opm/simulators/utils/MPIPacker.hpp
@@ -35,7 +35,9 @@ namespace Mpi {
 namespace detail {
 
 static std::size_t mpi_buffer_size(const std::size_t bufsize, const std::size_t position) {
-    assert (bufsize >= position);
+    if (bufsize < position)
+        throw std::invalid_argument("Buffer size should never be less than position!");
+
     return static_cast<int>(std::min(bufsize-position,
                                      static_cast<std::size_t>(std::numeric_limits<int>::max())));
 }
@@ -69,11 +71,10 @@ struct Packing<true,T>
     {
         // For now we do not handle the situation where a a single call to packSize/pack/unpack
         // is likely to require an MPI_Pack_size value larger than intmax
-        assert ( n*sizeof(T) <= std::numeric_limits<int>::max() );
+        if (n*sizeof(T) > std::numeric_limits<int>::max())
+            throw std::invalid_argument("packSize will be larger than max integer - this is not supported.");
         int size = 0;
         MPI_Pack_size(n, Dune::MPITraits<T>::getType(), comm, &size);
-        assert (size >= 0);
-        assert (size < std::numeric_limits<int>::max() );
         return static_cast<std::size_t>(size);
     }
 
diff --git a/opm/simulators/utils/MPISerializer.hpp b/opm/simulators/utils/MPISerializer.hpp
index 49729e4cd..1a12f07dd 100644
--- a/opm/simulators/utils/MPISerializer.hpp
+++ b/opm/simulators/utils/MPISerializer.hpp
@@ -52,15 +52,7 @@ public:
             try {
                 this->pack(data);
                 m_comm.broadcast(&m_packSize, 1, root);
-                const int maxChunkSize = std::numeric_limits<int>::max();
-                std::size_t remainingSize = m_packSize;
-                std::size_t pos = 0;
-                while (remainingSize > maxChunkSize) {
-                    m_comm.broadcast(m_buffer.data()+pos, maxChunkSize, root);
-                    pos += maxChunkSize;
-                    remainingSize -= maxChunkSize;
-                }
-                m_comm.broadcast(m_buffer.data()+pos, static_cast<int>(remainingSize), root);
+                broadcast_chunked(root);
             } catch (...) {
                 m_packSize = std::numeric_limits<size_t>::max();
                 m_comm.broadcast(&m_packSize, 1, root);
@@ -72,15 +64,7 @@ public:
                 throw std::runtime_error("Error detected in parallel serialization");
             }
             m_buffer.resize(m_packSize);
-            const int maxChunkSize = std::numeric_limits<int>::max();
-            std::size_t remainingSize = m_packSize;
-            std::size_t pos = 0;
-            while (remainingSize > maxChunkSize) {
-                m_comm.broadcast(m_buffer.data()+pos, maxChunkSize, root);
-                pos += maxChunkSize;
-                remainingSize -= maxChunkSize;
-            }
-            m_comm.broadcast(m_buffer.data()+pos, static_cast<int>(remainingSize), root);
+            broadcast_chunked(root);
             this->unpack(data);
         }
     }
@@ -95,15 +79,7 @@ public:
             try {
                 this->pack(std::forward<Args>(args)...);
                 m_comm.broadcast(&m_packSize, 1, root);
-                const int maxChunkSize = std::numeric_limits<int>::max();
-                std::size_t remainingSize = m_packSize;
-                std::size_t pos = 0;
-                while (remainingSize > maxChunkSize) {
-                    m_comm.broadcast(m_buffer.data()+pos, maxChunkSize, root);
-                    pos += maxChunkSize;
-                    remainingSize -= maxChunkSize;
-                }
-                m_comm.broadcast(m_buffer.data()+pos, static_cast<int>(remainingSize), root);
+                broadcast_chunked(root);
             } catch (...) {
                 m_packSize = std::numeric_limits<size_t>::max();
                 m_comm.broadcast(&m_packSize, 1, root);
@@ -115,15 +91,7 @@ public:
                 throw std::runtime_error("Error detected in parallel serialization");
             }
             m_buffer.resize(m_packSize);
-            const int maxChunkSize = std::numeric_limits<int>::max();
-            std::size_t remainingSize = m_packSize;
-            std::size_t pos = 0;
-            while (remainingSize > maxChunkSize) {
-                m_comm.broadcast(m_buffer.data()+pos, maxChunkSize, root);
-                pos += maxChunkSize;
-                remainingSize -= maxChunkSize;
-            }
-            m_comm.broadcast(m_buffer.data()+pos, static_cast<int>(remainingSize), root);
+            broadcast_chunked(root);
             this->unpack(std::forward<Args>(args)...);
         }
     }
@@ -149,6 +117,18 @@ public:
     }
 
 private:
+    void broadcast_chunked(int root) {
+        const int maxChunkSize = std::numeric_limits<int>::max();
+        std::size_t remainingSize = m_packSize;
+        std::size_t pos = 0;
+        while (remainingSize > maxChunkSize) {
+            m_comm.broadcast(m_buffer.data()+pos, maxChunkSize, root);
+            pos += maxChunkSize;
+            remainingSize -= maxChunkSize;
+        }
+        m_comm.broadcast(m_buffer.data()+pos, static_cast<int>(remainingSize), root);
+    }
+
     const Mpi::Packer m_packer; //!< Packer instance
     Parallel::Communication m_comm; //!< Communicator to use
 };