diff --git a/src/server/plugins/postcode-lookup/routes/index.js b/src/server/plugins/postcode-lookup/routes/index.js
index 2bd713d15..34feba53a 100644
--- a/src/server/plugins/postcode-lookup/routes/index.js
+++ b/src/server/plugins/postcode-lookup/routes/index.js
@@ -29,7 +29,9 @@ function getSessionState(request) {
   const state = request.yar.get(JOURNEY_BASE_URL)
 
   if (!state) {
-    throw Boom.internal(`No postcode lookup data found for ${JOURNEY_BASE_URL}`)
+    throw Boom.badRequest(
+      `No postcode lookup data found for ${JOURNEY_BASE_URL}`
+    )
   }
 
   return state