diff --git a/pytriqs/wrap_generator/wrap_generator.py b/pytriqs/wrap_generator/wrap_generator.py
index 3b7e4ff8..366bd23b 100644
--- a/pytriqs/wrap_generator/wrap_generator.py
+++ b/pytriqs/wrap_generator/wrap_generator.py
@@ -276,6 +276,7 @@ class class_ :
       # Init arithmetic
       # expect a tuple : "algebra", "scalar1", "scalar2", etc...
       self.number_protocol = {}
+      if not isinstance(arithmetic, tuple) : arithmetic = (arithmetic,)
       if arithmetic :
           if not isinstance(arithmetic, tuple) : arithmetic = (arithmetic,)
           add =  arithmetic[0] in ("algebra", "abelian_group", "vector_space", "only_add")
diff --git a/test/triqs/arrays/hdf5.cpp b/test/triqs/arrays/hdf5.cpp
index c7cfd2bd..c1e1829a 100644
--- a/test/triqs/arrays/hdf5.cpp
+++ b/test/triqs/arrays/hdf5.cpp
@@ -74,6 +74,8 @@ int main(int argc, char **argv) {
  h5_write(top,"C",C);
  h5_write(top,"D",D);
 
+ h5_write(top,"S","");
+ 
  // testing scalar
  double x=2.3;
  h5_write(top, "x",x);
diff --git a/triqs/h5/string.cpp b/triqs/h5/string.cpp
index dc0a03cb..1a0908f0 100644
--- a/triqs/h5/string.cpp
+++ b/triqs/h5/string.cpp
@@ -25,7 +25,7 @@ namespace triqs {
 
  void h5_write (group g, std::string const & name, std::string const & value) {
   try {
-   H5::StrType strdatatype(H5::PredType::C_S1, value.size());
+   H5::StrType strdatatype(H5::PredType::C_S1, value.size() + 1); // +1 for the 0 terminating char
    H5::DataSet ds = g.create_dataset(name, strdatatype, H5::DataSpace());
    ds.write((void*)(value.c_str()), strdatatype );
   }
diff --git a/triqs/parameters/_field.hpp b/triqs/parameters/_field.hpp
index 3c1aab71..43c1fcdf 100644
--- a/triqs/parameters/_field.hpp
+++ b/triqs/parameters/_field.hpp
@@ -173,7 +173,10 @@ namespace params {
 #ifdef TRIQS_WITH_PYTHON_SUPPORT
   /// Convertions python <-> C++
   bool from_python_convertible(PyObject *ob) const { return p->from_python_convertible(ob); }
-  void set_from_python(PyObject *ob) { p->set_from_python(ob); }
+  void set_from_python(PyObject *ob) {
+   p->set_from_python(ob);
+   modified = true;
+  }
   PyObject *to_python() const { return p->to_python(); }
 #endif