diff --git a/src/db/db/dbHierNetworkProcessor.cc b/src/db/db/dbHierNetworkProcessor.cc
index 0ef16ef41..c20e9c9d1 100644
--- a/src/db/db/dbHierNetworkProcessor.cc
+++ b/src/db/db/dbHierNetworkProcessor.cc
@@ -2945,10 +2945,23 @@ template <class T>
 void
 hier_clusters<T>::build_hier_connections_for_cells (cell_clusters_box_converter<T> &cbc, const db::Layout &layout, const std::vector<db::cell_index_type> &cells, const db::Connectivity &conn, const std::set<db::cell_index_type> *breakout_cells, tl::RelativeProgress &progress, instance_interaction_cache_type &instance_interaction_cache, bool separate_attributes)
 {
+#if defined(_OPENMP)
+  #pragma omp parallel for schedule(dynamic)
+  for (long long i = 0; i < (long long)cells.size (); ++i) {
+    db::cell_index_type c = cells[i];
+    build_hier_connections (cbc, layout, layout.cell (c), conn, breakout_cells, instance_interaction_cache, separate_attributes);
+    
+    #pragma omp critical
+    {
+      ++progress;
+    }
+  }
+#else
   for (std::vector<db::cell_index_type>::const_iterator c = cells.begin (); c != cells.end (); ++c) {
     build_hier_connections (cbc, layout, layout.cell (*c), conn, breakout_cells, instance_interaction_cache, separate_attributes);
     ++progress;
   }
+#endif
 }
 
 namespace {
diff --git a/src/db/db/dbHierNetworkProcessor.h b/src/db/db/dbHierNetworkProcessor.h
index e24605270..2176d1e07 100644
--- a/src/db/db/dbHierNetworkProcessor.h
+++ b/src/db/db/dbHierNetworkProcessor.h
@@ -1110,6 +1110,7 @@ public:
 
   size_t size () const
   {
+    tl::MutexLocker lock (&m_mutex);
     MemStatisticsSimple ms;
     ms << m_map;
     return ms.used ();
@@ -1127,6 +1128,7 @@ public:
 
   const Value *find (db::cell_index_type ci1, db::cell_index_type ci2, const Key &key) const
   {
+    tl::MutexLocker lock (&m_mutex);
     typename std::map <std::pair<db::cell_index_type, db::cell_index_type>, std::list <std::pair<Key, Value> > >::iterator i1 = m_map.find (std::make_pair (ci1, ci2));
     if (i1 == m_map.end ()) {
       ++m_misses;
@@ -1156,6 +1158,7 @@ public:
   {
     const size_t instance_cache_variant_threshold = 20;
 
+    tl::MutexLocker lock (&m_mutex);
     std::list <std::pair<Key, Value> > &m = m_map [std::make_pair (ci1, ci2)];
     if (m.size () >= instance_cache_variant_threshold) {
       m.pop_back ();
@@ -1166,6 +1169,7 @@ public:
   }
 
 private:
+  mutable tl::Mutex m_mutex;
   mutable size_t m_hits, m_misses;
   mutable std::map <std::pair<db::cell_index_type, db::cell_index_type>, std::list <std::pair<Key, Value> > > m_map;
 };