diff --git a/core/admin/mailu/models.py b/core/admin/mailu/models.py
index 95dc16a6..8176e461 100644
--- a/core/admin/mailu/models.py
+++ b/core/admin/mailu/models.py
@@ -27,7 +27,10 @@ class IdnaDomain(db.TypeDecorator):
     impl = db.String(80)
 
     def process_bind_param(self, value, dialect):
-        return idna.encode(value).decode("ascii").lower()
+        try:
+            return idna.encode(value).decode("ascii").lower()
+        except ValueError:
+            pass
 
     def process_result_value(self, value, dialect):
         return idna.decode(value)
diff --git a/towncrier/newsfragments/1087.bugfix b/towncrier/newsfragments/1087.bugfix
new file mode 100644
index 00000000..7d0ef69b
--- /dev/null
+++ b/towncrier/newsfragments/1087.bugfix
@@ -0,0 +1 @@
+Error handling in idna encoding