diff --git a/src/backend/concrete_history.cc b/src/backend/concrete_history.cc
index b49a772..abdeb3b 100644
--- a/src/backend/concrete_history.cc
+++ b/src/backend/concrete_history.cc
@@ -90,6 +90,13 @@ ConcreteHistory::~ConcreteHistory()
 	for_each(_snapshots.begin(), _snapshots.end(), ptr_fun(operator delete));
 }
 
+ConcreteHistory::ConcreteHistory(const ConcreteHistory& h) :
+  History(h)
+{
+  typedef Snapshots::const_iterator SnapIt;
+  for(SnapIt it = h._snapshots.begin(); it != h._snapshots.end(); ++it)
+    _snapshots.push_back(new ConcreteEnvironment(*(*it)));
+}
 
 void
 ConcreteHistory::append_new_environment(ConcreteEnvironment* environment)