diff --git a/prjxray/util.py b/prjxray/util.py
index 390e0c81..3fa592c5 100644
--- a/prjxray/util.py
+++ b/prjxray/util.py
@@ -71,3 +71,23 @@ def db_root_arg(parser):
         db_root_kwargs['required'] = False
         db_root_kwargs['default'] = os.path.join(database_dir, database)
     parser.add_argument('--db-root', help="Database root.", **db_root_kwargs)
+
+
+def parse_db_line(line):
+    parts = line.split()
+    # Ex: CLBLL_L.SLICEL_X0.AMUX.A5Q
+    assert len(parts), "Empty line"
+    tag = parts[0]
+    assert re.match(r'[A-Z0-9_.]+',
+                    tag), "Invalid tag name: %s, line: %s" % (tag, line)
+    orig_bits = line.replace(tag + " ", "")
+    # <0 candidates> etc
+    if "<" in orig_bits:
+        return tag, set(), orig_bits
+
+    # Ex: !30_06 !30_08 !30_11 30_07
+    bits = frozenset(parts[1:])
+    for bit in bits:
+        assert re.match(
+            r'[!]*[0-9][0-9]_[0-9][0-9]', bit), "Invalid bit: %s" % bit
+    return tag, bits, None
diff --git a/utils/dbfixup.py b/utils/dbfixup.py
index 1dd5f872..4f069da7 100755
--- a/utils/dbfixup.py
+++ b/utils/dbfixup.py
@@ -17,20 +17,6 @@ clb_int_zero_db = [
 ]
 
 
-def parse_line(line):
-    parts = line.split()
-    # Ex: CLBLL_L.SLICEL_X0.AMUX.A5Q
-    tag = parts[0]
-    orig_bits = line.replace(tag + " ", "")
-    # <0 candidates> etc
-    if "<" in orig_bits:
-        return tag, set(), orig_bits
-
-    # Ex: !30_06 !30_08 !30_11 30_07
-    bits = set(parts[1:])
-    return tag, bits, None
-
-
 def zero_range(bits, wordmin, wordmax):
     """
     If any bits occur wordmin <= word <= wordmax,
@@ -134,7 +120,7 @@ def add_zero_bits(fn_in, fn_out, zero_db, clb_int=False, verbose=False):
             if line == llast:
                 continue
 
-            tag, bits, mode = parse_line(line)
+            tag, bits, mode = util.parse_db_line(line)
             assert mode not in (
                 "<const0>",
                 "<const1>"), "Entries must be resolved. line: %s" % (line, )
@@ -146,6 +132,7 @@ def add_zero_bits(fn_in, fn_out, zero_db, clb_int=False, verbose=False):
             """
             if clb_int:
                 zero_range(bits, 22, 25)
+            bits = set(bits)
             zero_groups(
                 tag, bits, zero_db, strict=not clb_int, verbose=verbose)
 
diff --git a/utils/environment.sh b/utils/environment.sh
index fb69da52..76b1e6bb 100644
--- a/utils/environment.sh
+++ b/utils/environment.sh
@@ -26,4 +26,5 @@ export XRAY_BITS2FASM="python3 ${XRAY_UTILS_DIR}/bits2fasm.py"
 export XRAY_FASM2FRAMES="python3 ${XRAY_UTILS_DIR}/fasm2frames.py"
 export XRAY_BITTOOL="${XRAY_TOOLS_DIR}/bittool"
 export XRAY_BLOCKWIDTH="python3 ${XRAY_UTILS_DIR}/blockwidth.py"
+export XRAY_PARSEDB="python3 ${XRAY_UTILS_DIR}/parsedb.py"
 
diff --git a/utils/mergedb.sh b/utils/mergedb.sh
index 391d3e40..848d50f3 100755
--- a/utils/mergedb.sh
+++ b/utils/mergedb.sh
@@ -71,6 +71,6 @@ esac
 
 touch "$db"
 sort -u "$tmp1" "$db" | grep -v '<.*>' > "$tmp2" || true
-mv "$tmp2" "$db"
+${XRAY_PARSEDB} --strict "$tmp2" "$db"
 rm -f "$tmp1"
 
diff --git a/utils/parsedb.py b/utils/parsedb.py
new file mode 100755
index 00000000..e3837798
--- /dev/null
+++ b/utils/parsedb.py
@@ -0,0 +1,53 @@
+#!/usr/bin/env python3
+
+from prjxray import util
+
+
+def run(fnin, fnout=None, strict=False, verbose=False):
+    lines = open(fnin, 'r').read().split('\n')
+    tags = set()
+    bitss = set()
+    for line in lines:
+        line = line.strip()
+        if line == '':
+            continue
+        tag, bits, mode = util.parse_db_line(line)
+        if strict:
+            assert not mode, "strict: got ill defined line: %s" % (line, )
+            assert tag not in tags, "strict: got duplicate tag %s (ex: %s)" % (
+                tag, line)
+            assert bits not in bitss, "strict: got duplicate bits %s (ex: %s)" % (
+                bits, line)
+        tags.add(tag)
+        bitss.add(bits)
+
+    if fnout:
+        with open(fnout, "w") as fout:
+            for line in sorted(lines):
+                line = line.strip()
+                if line == '':
+                    continue
+                fout.write(line + '\n')
+
+
+def main():
+    import argparse
+
+    parser = argparse.ArgumentParser(
+        description="Parse a db, check for consistency")
+
+    util.db_root_arg(parser)
+    parser.add_argument('--verbose', action='store_true', help='')
+    parser.add_argument(
+        '--strict',
+        action='store_true',
+        help='Complain on unresolved entries (ex: <0 candidates>, <const0>)')
+    parser.add_argument('fin', help='')
+    parser.add_argument('fout', nargs='?', help='')
+    args = parser.parse_args()
+
+    run(args.fin, args.fout, strict=args.strict, verbose=args.verbose)
+
+
+if __name__ == '__main__':
+    main()