diff --git a/d3/model/formats/obj.py b/d3/model/formats/obj.py
index 26ec05d..ae0338b 100644
--- a/d3/model/formats/obj.py
+++ b/d3/model/formats/obj.py
@@ -61,6 +61,9 @@ class OBJParser(TextModelParser):
                             splits[i][j] -= 1
                         else:
                             splits[i][j] = len(self.vertices) + splits[i][j]
+                    elif j == 1:
+                        # Here, splits[i][j] == '', so we must set the value to None
+                        splits[i][j] = None
 
             # if Face3
             if len(split) == 3: