diff --git a/libsrc/core/archive.hpp b/libsrc/core/archive.hpp
index 1fedde76..8c45baf2 100644
--- a/libsrc/core/archive.hpp
+++ b/libsrc/core/archive.hpp
@@ -153,6 +153,9 @@ namespace ngcore
     const VersionInfo& GetVersion(const std::string& library)
     { return version_map[library]; }
 
+    // only used for PyArchive
+    virtual void NeedsVersion(const std::string& library, const std::string& version) {}
+
     // Pure virtual functions that have to be implemented by In-/OutArchive
     virtual Archive & operator & (double & d) = 0;
     virtual Archive & operator & (int & i) = 0;
@@ -900,6 +903,7 @@ namespace ngcore
   private:
     pybind11::list lst;
     size_t index = 0;
+    std::map<std::string, VersionInfo> version_needed;
   protected:
     using ARCHIVE::stream;
     using ARCHIVE::version_map;
@@ -915,9 +919,26 @@ namespace ngcore
         {
           stream = std::make_shared<std::stringstream>
             (pybind11::cast<pybind11::bytes>(lst[pybind11::len(lst)-1]));
-          *this & version_map;
+          *this & version_needed;
+          logger->debug("versions needed for unpickling = {}", version_needed);
+          for(auto& libversion : version_needed)
+            if(libversion.second > GetLibraryVersion(libversion.first))
+              throw Exception("Error in unpickling data:\nLibrary " + libversion.first +
+                              " must be at least " + libversion.second.to_string());
           stream = std::make_shared<std::stringstream>
             (pybind11::cast<pybind11::bytes>(lst[pybind11::len(lst)-2]));
+          *this & version_map;
+          stream = std::make_shared<std::stringstream>
+            (pybind11::cast<pybind11::bytes>(lst[pybind11::len(lst)-3]));
+        }
+    }
+
+    void NeedsVersion(const std::string& library, const std::string& version) override
+    {
+      if(Output())
+        {
+          logger->debug("Need version {} of library {}.", version, library);
+          version_needed[library] = version_needed[library] > version ? version_needed[library] : version;
         }
     }
 
@@ -936,6 +957,12 @@ namespace ngcore
       lst.append(pybind11::bytes(std::static_pointer_cast<std::stringstream>(stream)->str()));
       stream = std::make_shared<std::stringstream>();
       *this & GetLibraryVersions();
+      FlushBuffer();
+      lst.append(pybind11::bytes(std::static_pointer_cast<std::stringstream>(stream)->str()));
+      stream = std::make_shared<std::stringstream>();
+      logger->debug("Writeout version needed = {}", version_needed);
+      *this & version_needed;
+      FlushBuffer();
       lst.append(pybind11::bytes(std::static_pointer_cast<std::stringstream>(stream)->str()));
       return lst;
     }
@@ -949,17 +976,17 @@ namespace ngcore
                         PyArchive<T_ARCHIVE_OUT> ar;
                         ar & self;
                         auto output = pybind11::make_tuple(ar.WriteOut());
-                        NETGEN_DEBUG_LOG(GetLogger("Archive"), "pickling output for object of type " +
-                                         Demangle(typeid(T).name()) + " = " +
-                                         std::string(pybind11::str(output)));
+                        GetLogger("Archive")->trace("Pickling output for object of type {} = {}",
+                                                    Demangle(typeid(T).name()),
+                                                    std::string(pybind11::str(output)));
                         return output;
                       },
                       [](pybind11::tuple state)
                       {
                         T* val = nullptr;
-                        NETGEN_DEBUG_LOG(GetLogger("Archive"), "State for unpickling of object of type " +
-                                         Demangle(typeid(T).name()) + " = " +
-                                         std::string(pybind11::str(state[0])));
+                        GetLogger("Archive")->trace("State for unpickling of object of type {} = {}",
+                                                    Demangle(typeid(T).name()),
+                                                    std::string(pybind11::str(state[0])));
                         PyArchive<T_ARCHIVE_IN> ar(state[0]);
                         ar & val;
                         return val;
diff --git a/libsrc/core/utils.hpp b/libsrc/core/utils.hpp
index da90e1d3..f2a73578 100644
--- a/libsrc/core/utils.hpp
+++ b/libsrc/core/utils.hpp
@@ -2,6 +2,8 @@
 #define NETGEN_CORE_UTILS_HPP
 
 #include <chrono>
+#include <map>
+#include <ostream>
 #include <sstream>
 #include <string>
 
@@ -56,7 +58,13 @@ namespace ngcore
       return ss.str();
   }
 
-
+  template<typename T1, typename T2>
+  std::ostream& operator << (std::ostream& ost, const std::map<T1,T2>& map)
+  {
+    for(auto& val : map)
+      ost << "\n" << val.first << ": " << val.second;
+    return ost;
+  }
 } // namespace ngcore
 
 #endif // NETGEN_CORE_UTILS_HPP
diff --git a/libsrc/core/version.hpp b/libsrc/core/version.hpp
index 69598716..aea50bf6 100644
--- a/libsrc/core/version.hpp
+++ b/libsrc/core/version.hpp
@@ -1,6 +1,7 @@
 #ifndef NETGEN_CORE_VERSION_HPP
 #define NETGEN_CORE_VERSION_HPP
 
+#include <ostream>
 #include <string>
 #include <tuple>
 
@@ -83,6 +84,11 @@ namespace ngcore
     bool operator <=(const VersionInfo& other) const { return !((*this) > other); }
     bool operator >=(const VersionInfo& other) const { return !((*this) < other); }
   };
+
+  inline std::ostream& operator << (std::ostream& ost, const VersionInfo& version)
+  {
+    return ost << version.to_string();
+  }
 } // namespace ngcore
 
 #endif // NETGEN_CORE_VERSION_HPP
diff --git a/tests/catch/archive.cpp b/tests/catch/archive.cpp
index b3f27d49..60cd33f0 100644
--- a/tests/catch/archive.cpp
+++ b/tests/catch/archive.cpp
@@ -236,6 +236,18 @@ void testMultipleInheritance(Archive& in, Archive& out)
     }
 }
 
+void testMap(Archive& in, Archive& out)
+{
+  map<string, VersionInfo> map1;
+  map1["netgen"] = "v6.2.1901";
+  out & map1;
+  out.FlushBuffer();
+  map<string, VersionInfo> map2;
+  in & map2;
+  CHECK(map2.size() == 1);
+  CHECK(map2["netgen"] == "v6.2.1901");
+}
+
 void testArchive(Archive& in, Archive& out)
 {
   SECTION("Empty String")
@@ -285,11 +297,14 @@ void testArchive(Archive& in, Archive& out)
     {
       testNullPtr(in, out);
     }
+  SECTION("map")
+    {
+      testMap(in, out);
+    }
 }
 
 TEST_CASE("BinaryArchive")
 {
-  SetLibraryVersion("netgen","v6.2.1811");
   auto stream = make_shared<stringstream>();
   BinaryOutArchive out(stream);
   BinaryInArchive in(stream);
@@ -298,7 +313,6 @@ TEST_CASE("BinaryArchive")
 
 TEST_CASE("TextArchive")
 {
-  SetLibraryVersion("netgen","v6.2.1811");
   auto stream = make_shared<stringstream>();
   TextOutArchive out(stream);
   TextInArchive in(stream);