diff --git a/isso/db/__init__.py b/isso/db/__init__.py
index d3831867..71b8ef6a 100644
--- a/isso/db/__init__.py
+++ b/isso/db/__init__.py
@@ -22,7 +22,7 @@ class SQLite3:
     a trigger for automated orphan removal.
     """
 
-    MAX_VERSION = 3
+    MAX_VERSION = 4
 
     def __init__(self, path, conf):
 
@@ -121,3 +121,39 @@ def first(rv):
 
                 con.execute('PRAGMA user_version = 3')
                 logger.info("%i rows changed", con.total_changes)
+
+        # "text" field in "comments" became NOT NULL
+        if self.version == 3:
+            with sqlite3.connect(self.path) as con:
+                con.execute("BEGIN TRANSACTION")
+                con.execute("UPDATE comments SET text = '' WHERE text IS NULL")
+                logger.info("%i rows changed", con.total_changes)
+
+                # create new table with NOT NULL constraint for "text" field
+                con.execute('CREATE TABLE IF NOT EXISTS comments_new ('
+                            '    tid REFERENCES threads(id), id INTEGER PRIMARY KEY, parent INTEGER,'
+                            '    created FLOAT NOT NULL, modified FLOAT, mode INTEGER, remote_addr VARCHAR,'
+                            '    text VARCHAR NOT NULL, author VARCHAR, email VARCHAR, website VARCHAR,'
+                            '    likes INTEGER DEFAULT 0, dislikes INTEGER DEFAULT 0, voters BLOB NOT NULL,'
+                            '    notification INTEGER DEFAULT 0);')
+
+                try:
+                    # copy data from old table to new table
+                    con.execute("""
+                        INSERT INTO comments_new (
+                            tid, id, parent, created, modified, mode, remote_addr, text, author, email, website, likes, dislikes, voters, notification
+                        )
+                        SELECT
+                            tid, id, parent, created, modified, mode, remote_addr, text, author, email, website, likes, dislikes, voters, notification
+                        FROM comments
+                    """)
+
+                    # swap tables
+                    con.execute("ALTER TABLE comments RENAME TO comments_backup_v3")
+                    con.execute("ALTER TABLE comments_new RENAME TO comments")
+
+                    con.execute('PRAGMA user_version = 4')
+                    con.execute("COMMIT")
+                except sqlite3.Error as e:
+                    con.execute("ROLLBACK")
+                    logger.error("Database migration to version 4 failed: %s", e)
diff --git a/isso/tests/test_db.py b/isso/tests/test_db.py
index 09860f17..8c4e50d2 100644
--- a/isso/tests/test_db.py
+++ b/isso/tests/test_db.py
@@ -82,19 +82,19 @@ def test_limit_nested_comments(self):
                         "    id INTEGER PRIMARY KEY,"
                         "    parent INTEGER,"
                         "    created FLOAT NOT NULL, modified FLOAT,"
-                        "    text VARCHAR, email VARCHAR, website VARCHAR,"
+                        "    text VARCHAR, author VARCHAR, email VARCHAR, website VARCHAR,"
                         "    mode INTEGER,"
                         "    remote_addr VARCHAR,"
                         "    likes INTEGER DEFAULT 0,"
                         "    dislikes INTEGER DEFAULT 0,"
-                        "    voters BLOB)")
+                        "    voters BLOB NOT NULL)")
 
             con.execute(
                 "INSERT INTO threads (uri, title) VALUES (?, ?)", ("/", "Test"))
             for (id, parent) in tree.items():
                 con.execute("INSERT INTO comments ("
-                            "   id, parent, created)"
-                            "VALUEs (?, ?, ?)", (id, parent, id))
+                            "   id, parent, created, voters)"
+                            "VALUEs (?, ?, ?, ?)", (id, parent, id, sqlite3.Binary(b"")))
 
         conf = config.new({
             "general": {
@@ -118,3 +118,58 @@ def test_limit_nested_comments(self):
             rv = con.execute(
                 "SELECT id, parent FROM comments ORDER BY created").fetchall()
             self.assertEqual(flattened, rv)
+
+    def test_comment_text_not_null_migration(self):
+        conf = config.new({
+            "general": {
+                "dbpath": "/dev/null",
+                "max-age": "1h"
+            }
+        })
+
+        with sqlite3.connect(self.path) as con:
+            con.execute("PRAGMA user_version = 3")
+
+            con.execute("CREATE TABLE threads ("
+                        "    id INTEGER PRIMARY KEY,"
+                        "    uri VARCHAR UNIQUE,"
+                        "    title VARCHAR)")
+            con.execute("CREATE TABLE comments ("
+                        "    tid REFERENCES threads(id),"
+                        "    id INTEGER PRIMARY KEY,"
+                        "    parent INTEGER,"
+                        "    created FLOAT NOT NULL, modified FLOAT,"
+                        "    text VARCHAR, author VARCHAR, email VARCHAR, website VARCHAR,"
+                        "    mode INTEGER,"
+                        "    remote_addr VARCHAR,"
+                        "    likes INTEGER DEFAULT 0,"
+                        "    dislikes INTEGER DEFAULT 0,"
+                        "    voters BLOB NOT NULL)")
+
+            con.execute(
+                "INSERT INTO threads (uri, title) VALUES (?, ?)", ("/", "Test"))
+
+            con.execute("INSERT INTO comments (id, parent, created, text, voters) VALUES (?, ?, ?, ?, ?)",
+                        (1, None, 1, None, sqlite3.Binary(b"")))
+
+            con.execute("INSERT INTO comments (id, parent, created, text, voters) VALUES (?, ?, ?, ?, ?)",
+                        (2, 1, 2, "foo", sqlite3.Binary(b"")))
+
+        conf = config.new({
+            "general": {
+                "dbpath": "/dev/null",
+                "max-age": "1h"
+            }
+        })
+
+        db = SQLite3(self.path, conf)
+
+        self.assertEqual(db.version, SQLite3.MAX_VERSION)
+
+        with sqlite3.connect(self.path) as con:
+            # assert that the "text" field has "NOT NULL" constraint
+            rv = con.execute("SELECT \"notnull\" FROM pragma_table_info('comments') WHERE name='text'").fetchone()
+            self.assertEqual(rv, (1,))
+
+            rv = con.execute("SELECT text FROM comments WHERE id IN (1, 2)").fetchall()
+            self.assertEqual(rv, [("",), ("foo",)])