diff --git a/lib/mdb/db.py b/lib/mdb/db.py
index c5622fd..d326710 100644
--- a/lib/mdb/db.py
+++ b/lib/mdb/db.py
@@ -65,6 +65,8 @@ class PVVDB:
                 continue
             name, value    = line.strip().split(":", 1)
             value          = value.split("#", 1)[0].strip()
+            if not value in ['scalar', 'list']:
+                raise PVVDBError, "%s not legal .format datatype." % value
             fmt[name] = value
         return fmt