diff --git a/soitool/database.py b/soitool/database.py
index ae05d7864dad8057599f2e961fb3ee91c25f04a3..6e998717b7fce6540b5acc5536f9b2e844156cca 100644
--- a/soitool/database.py
+++ b/soitool/database.py
@@ -11,7 +11,8 @@ DBPATH = os.path.join(CURDIR, DBNAME)
 
 # DDL-statements for creating tables
 CODEBOOK = "CREATE TABLE CodeBook" \
-           "(Word VARCHAR PRIMARY KEY NOT NULL, Category VARCHAR, " \
+           "(Word VARCHAR PRIMARY KEY NOT NULL CHECK(length(Word) > 0), " \
+           "Category VARCHAR, " \
            "Type VARCHAR DEFAULT 'Stor' CHECK(Type='Stor' OR Type='Liten'), " \
            "Code VARCHAR UNIQUE)"
 CATEGORYWORDS = "CREATE TABLE CategoryWords" \