diff --git a/prjxray/util.py b/prjxray/util.py
index 0b4cf689..7cde6a0c 100644
--- a/prjxray/util.py
+++ b/prjxray/util.py
@@ -189,15 +189,19 @@ def gen_tile_bits(db_root, tilej, strict=False, verbose=False):
     for block_type, blockj in tilej["bits"].items():
         baseaddr = int(blockj["baseaddr"], 0)
         bitbase = 32 * blockj["offset"]
+        frames = tilej["bits"][block_type]["frames"]
 
         if block_type == "CLB_IO_CLK":
             fn = "%s/segbits_%s.db" % (db_root, tilej["type"].lower())
         else:
-            fn = "%s/segbits_%s.db.%s" % (
+            fn = "%s/segbits_%s.%s.db" % (
                 db_root, tilej["type"].lower(), block_type.lower())
         # tilegrid runs a lot earlier than fuzzers
         # may not have been created yet
         verbose and print("Check %s: %s" % (fn, os.path.exists(fn)))
+
+        # FIXME: some segbits files are not present and the strict check produces assertion errors
+        # e.g. segbits_cmt_top_r_lower_b.db
         if strict:
             assert os.path.exists(fn)
         elif not os.path.exists(fn):
@@ -208,6 +212,7 @@ def gen_tile_bits(db_root, tilej, strict=False, verbose=False):
             for bitstr in bits:
                 # 31_06
                 _bit_inv, (bit_addroff, bit_bitoff) = parse_tagbit(bitstr)
+                assert bit_addroff <= frames, "ERROR: bit out of bound"
                 yield (baseaddr + bit_addroff, bitbase + bit_bitoff, tag)
 
 
diff --git a/utils/checkdb.py b/utils/checkdb.py
index 425cf4d6..df1d8090 100755
--- a/utils/checkdb.py
+++ b/utils/checkdb.py
@@ -64,6 +64,7 @@ def check_tile_overlap(db, db_root, strict=False, verbose=False):
     Throw an exception if two tiles share an address
     '''
     mall = dict()
+    tiles_type_done = set()
 
     tiles_checked = 0
 
@@ -74,6 +75,10 @@ def check_tile_overlap(db, db_root, strict=False, verbose=False):
     for tile_name, tilej in db.tilegrid.items():
         # for tile_name, tilej in subtiles(["CLBLL_L_X14Y112", "INT_L_X14Y112"]):
 
+        if tilej['type'] in tiles_type_done or not tilej["bits"]:
+            continue
+        tiles_type_done.add(tilej['type'])
+
         mtile = make_tile_mask(
             db_root, tile_name, tilej, strict=strict, verbose=verbose)
         verbose and print(