fix #2453

sapl/materia/forms.py

@@ -202,6 +202,7 @@ class MateriaLegislativaForm(ModelForm):
                                                         widget=forms.HiddenInput())
             self.fields['autor'] = forms.CharField(required=False,
                                                    widget=forms.HiddenInput())
+            if kwargs['instance'].numero_protocolo:
                 self.fields['numero_protocolo'].widget.attrs['readonly'] = True
 
     def clean(self):