diff --git a/ipv6ula/models.py b/ipv6ula/models.py
index 772985f..252af72 100644
--- a/ipv6ula/models.py
+++ b/ipv6ula/models.py
@@ -14,7 +14,7 @@ def validate_ula_prefix(prefix):
 
     if not net.subnet_of(ula_net):
         raise ValidationError(
-            _(f"Prefix {prefix} is not within ULA range ({ula_net})"),
+            _(f"Prefix {net} is not within ULA range ({ula_net})"),
             code='invalid',
             params = {'prefix': net }
         )