diff --git a/kibot/kicad/v6_sch.py b/kibot/kicad/v6_sch.py
index 2eb5083e..9a354991 100644
--- a/kibot/kicad/v6_sch.py
+++ b/kibot/kicad/v6_sch.py
@@ -1049,7 +1049,7 @@ class SchematicV6(Schematic):
                 error = str(e)
             if error:
                 raise SchError(error)
-        if sch[0].value() != 'kicad_sch':
+        if not isinstance(sch, list) or sch[0].value() != 'kicad_sch':
             raise SchError('No kicad_sch signature')
         for e in sch[1:]:
             e_type = _check_is_symbol_list(e)