diff --git a/modules/io/src/mol/pdb_writer.cc b/modules/io/src/mol/pdb_writer.cc
index 17f891d57226ae479893a854f302008e16d7b231..6f9c01cb928322b48d9c03a13fe34cd814638abb 100644
--- a/modules/io/src/mol/pdb_writer.cc
+++ b/modules/io/src/mol/pdb_writer.cc
@@ -78,7 +78,12 @@ void write_atom(std::ostream& ostr, FormattedLine& line,
   
   geom::Vec3 p=atom.GetPos();
   line( 0, 6)=record_name;
-  line( 6, 5)=fmt::LPaddedInt(atomnum);
+  // Avoid writing out atomnumbers larger than 5 digits
+  if (atomnum > 99999) {
+    line( 6, 5)=fmt::LPaddedInt(atomnum - 100000 * (atomnum / 100000));
+  } else {
+    line( 6, 5)=fmt::LPaddedInt(atomnum);
+  }
   String atom_name=atom.GetName();
   if (atom_name.size()>4) {
     throw IOException("Atom name '"+atom.GetQualifiedName()+