diff --git a/edgehog/edgehog.py b/edgehog/edgehog.py
index b8cdc10..7e3d2bc 100644
--- a/edgehog/edgehog.py
+++ b/edgehog/edgehog.py
@@ -31,7 +31,6 @@ def main():
     arg_parser.add_argument('--max_gaps', type=int, help='max_gaps can be seen as the theoritical maximal number of consecutive novel genes that can emerge between two older genes (default = 3), '
                             'e.g.  if max_gaps = 2: the probabilistic A-b-c-D-E-f-g-h-I-J graph will be turn into A-D-E ; I-J in the ancestor'
                             'while if max_gaps = 3: the probabilistic A-b-c-D-E-f-g-h-I-J graph will be turn into A-D-E-I-J   in the ancestor', default=3)
-    # arg_parser.add_argument('--cpu', type=str, default='1', help='number of CPUs to use (default is 1)')
     arg_parser.add_argument('--include_extant_genes', action='store_true', help='include extant genes in output file for ancestral reconstructions.')
     arg_parser.add_argument("--out-format", choices=("TSV", "HDF5"), default="TSV",
                             help="define output format. Can be TSV (tab seperated files) or HDF5 (compatible for integration into oma hdf5)")
diff --git a/edgehog/hdf5.py b/edgehog/hdf5.py
index 4caa839..f84711e 100644
--- a/edgehog/hdf5.py
+++ b/edgehog/hdf5.py
@@ -8,6 +8,7 @@
     from pyoma.browser.tablefmt import AncestralSyntenyRels
     from pyoma.browser import db
     from pyoma.browser.models import Genome
+    from pyoma import version as pyoma_version
 except ImportError:
     print(f"pyoma and pytables libraries are required to work on HDF5 files. "
           f"Please install edgehog with the `oma` extras added, i.e. `pip install edgehog[oma]`.")
@@ -43,16 +44,14 @@ def _load_hog_at_level(self, taxid):
         return {row['ID'].decode(): row_nr for row_nr, row in enumerate(tab.read())}
 
     def add_graph_at_level(self, taxid, tree_node):
-        try:
-            from pyoma.browser.tablefmt import AncestralSyntenyRels
-        except ImportError:
-            print(f"pyoma library is required to write output as HDF5 files. "
-                  f"Please install edgehog with the `oma` extra activated, i.e. `pip install edgehog[oma]`.")
-            import sys
-            sys.exit(2)
         hogid_lookup = self._load_hog_at_level(taxid)
         dtype = tables.dtype_from_descr(AncestralSyntenyRels)
-        orient_enum = AncestralSyntenyRels.columns['Orientation'].enum
+        if self.orient_edges:
+            try:
+                orient_enum = AncestralSyntenyRels.columns['Orientation'].enum
+            except KeyError:
+                print(f"[WARNING] The installed pyoma library ({pyoma_version()}) does not allow to store the Orientation results. Please update pyoma if needed")
+                self.orient_edges = False
         dfs = []
         for evidence, graph in zip(
                 ("linearized", "parsimonious", "any"),
@@ -62,7 +61,7 @@ def add_graph_at_level(self, taxid, tree_node):
             print(f"process level {taxid} - graph {evidence} - |N|,|V| = {len(graph.nodes)},{len(graph.edges)}")
 
             for u, v, edge_data in graph.edges.data():
-                w = edge_data.get("weight", default=1)
+                w = edge_data["weight"]
                 h1 = u.hog_id.rsplit('_')[0]
                 h2 = v.hog_id.rsplit('_')[0]
                 lca, orient, orient_score = -1, -1, 0