diff -up xdrawchem-1.9.9/xdrawchem/molecule_obmol.cpp.gcc6 xdrawchem-1.9.9/xdrawchem/molecule_obmol.cpp

--- xdrawchem-1.9.9/xdrawchem/molecule_obmol.cpp.gcc6	2005-11-30 03:55:06.000000000 +0100

+++ xdrawchem-1.9.9/xdrawchem/molecule_obmol.cpp	2016-02-17 16:03:30.652748203 +0100

@@ -198,7 +198,7 @@ OBMol * Molecule::convertToOBMol() {

     atom.SetType( type );

     if (!obmol->AddAtom(atom))

-      return(false);

+      return(NULL);

     atom.Clear();

   }

@@ -212,7 +212,7 @@ OBMol * Molecule::convertToOBMol() {

     bst = tmp_bond->Stereo();

     if (bst == STEREO_UP) flag |= OB_WEDGE_BOND;

     if (bst == STEREO_DOWN) flag |= OB_HASH_BOND;

-    if (!obmol->AddBond(start,end,order,flag)) return(false);

+    if (!obmol->AddBond(start,end,order,flag)) return(NULL);

   }

   obmol->EndModify();