diff --git a/pycrate_asn1rt/asnobj_construct.py b/pycrate_asn1rt/asnobj_construct.py
index 8d0a711..f003698 100644
--- a/pycrate_asn1rt/asnobj_construct.py
+++ b/pycrate_asn1rt/asnobj_construct.py
@@ -2214,6 +2214,8 @@ class _CONSTRUCT_OF(ASN1Obj):
         #self._cont._val = None
     
     def _to_per_ws(self):
+        if not self._val:
+            return []
         GEN, ldet = [], len(self._val)
         if self._const_sz:
             if self._const_sz.ext is not None:
@@ -2302,6 +2304,8 @@ class _CONSTRUCT_OF(ASN1Obj):
         self._struct = Envelope(self._name, GEN=tuple(GEN))
            
     def _to_per(self):
+        if not self._val:
+            return []
         GEN, ldet = [], len(self._val)
         if self._const_sz:
             if self._const_sz.ext is not None: