diff --git a/fuzzers/005-tilegrid/add_tdb.py b/fuzzers/005-tilegrid/add_tdb.py
index e526f38d..f185259a 100644
--- a/fuzzers/005-tilegrid/add_tdb.py
+++ b/fuzzers/005-tilegrid/add_tdb.py
@@ -37,6 +37,7 @@ def load_db(fn):
         parts = l.split(' ')
         tagstr = parts[0]
         addrlist = parts[1:]
+        assert not any(s == '<const0>' for s in addrlist), (fn, l)
         check_frames(tagstr, addrlist)
         # Take the first address in the list
         frame, wordidx, bitidx = parse_addr(addrlist[0])