diff --git a/netbox/dcim/forms.py b/netbox/dcim/forms.py
index e4effaed6..933e6b626 100644
--- a/netbox/dcim/forms.py
+++ b/netbox/dcim/forms.py
@@ -1607,7 +1607,7 @@ class InterfaceCSVForm(forms.ModelForm):
                 device=device_id, form_factor=IFACE_FF_LAG).get(
                 lag=lag_name.id
             )
-        if not self.data('lag'):
+        if lag is not None:
             return None
         return lag