diff --git a/src/testing/test_bank_api_twisted.c b/src/testing/test_bank_api_twisted.c
index 73e82bfc7..8ca98948d 100644
--- a/src/testing/test_bank_api_twisted.c
+++ b/src/testing/test_bank_api_twisted.c
@@ -84,7 +84,7 @@ run (void *cls,
 {
   struct TALER_WireTransferIdentifierRawP wtid;
 
-  memset (&wtid, 0x5aff, sizeof (wtid));
+  memset (&wtid, 0x5a, sizeof (wtid));
 
   /* Route our commands through twister. */
   struct TALER_BANK_AuthenticationData exchange_auth_twisted;