diff --git a/test/property/test_webhook_handler.rb b/test/property/test_webhook_handler.rb
index 3a30b203fb101030f5f0d5c3c65c42594b9408c2..61a4275262182f494dee2a88fdd2f3056d4b137c 100644
--- a/test/property/test_webhook_handler.rb
+++ b/test/property/test_webhook_handler.rb
@@ -101,4 +101,25 @@ class WebhookPropertyTest < Minitest::Test
 		}
 	end
 	em :test_single_recipient_message_failed_sends_one_error
+
+	def test_outbound_unregistered_returns_403
+		property_of {
+			Webhook
+				.new(REDIS)
+				.registered {
+					false
+				}
+				.type {
+					choose(*Webhook::OUTBOUND_TYPES)
+				}
+				.generate
+		}.check { |metadata, example|
+			result = invoke_webhook(example)
+			assert_equal [403, {}, "Customer not found\n"], result
+			assert_empty written
+			entries = REDIS.stream_entries("messages").sync
+			assert_empty entries
+		}
+	end
+	em :test_outbound_unregistered_returns_403
 end