diff --git a/src/Simplex/Messaging/Agent/Store/SQLite/Schema.hs b/src/Simplex/Messaging/Agent/Store/SQLite/Schema.hs
index e7a0b2d9e..47f0e255d 100644
--- a/src/Simplex/Messaging/Agent/Store/SQLite/Schema.hs
+++ b/src/Simplex/Messaging/Agent/Store/SQLite/Schema.hs
@@ -12,8 +12,8 @@ servers =
   [s|
     CREATE TABLE IF NOT EXISTS servers
       ( server_id INTEGER PRIMARY KEY,
-        host_address TEXT,
-        port INT,
+        host_address TEXT NOT NULL,
+        port INT NOT NULL,
         key_hash BLOB,
         UNIQUE (host_address, port)
       )
@@ -25,15 +25,17 @@ recipientQueues =
   [s|
     CREATE TABLE IF NOT EXISTS recipient_queues
       ( recipient_queue_id INTEGER PRIMARY KEY,
-        server_id INTEGER REFERENCES servers(server_id),
-        rcv_id BLOB,
-        rcv_private_key BLOB,
+        server_id INTEGER REFERENCES servers(server_id) NOT NULL,
+        rcv_id BLOB NOT NULL,
+        rcv_private_key BLOB NOT NULL,
         snd_id BLOB,
         snd_key BLOB,
-        decrypt_key BLOB,
+        decrypt_key BLOB NOT NULL,
         verify_key BLOB,
-        status TEXT,
-        ack_mode INTEGER
+        status TEXT NOT NULL,
+        ack_mode INTEGER NOT NULL,
+        UNIQUE (server_id, rcv_id),
+        UNIQUE (server_id, snd_id)
       )
   |]
 
@@ -42,13 +44,13 @@ senderQueues =
   [s|
     CREATE TABLE IF NOT EXISTS sender_queues
       ( sender_queue_id INTEGER PRIMARY KEY,
-        server_id INTEGER REFERENCES servers(server_id),
-        snd_id BLOB,
-        snd_private_key BLOB,
-        encrypt_key BLOB,
-        sign_key BLOB,
-        status TEXT,
-        ack_mode INTEGER
+        server_id INTEGER REFERENCES servers(server_id) NOT NULL,
+        snd_id BLOB NOT NULL,
+        snd_private_key BLOB NOT NULL,
+        encrypt_key BLOB NOT NULL,
+        sign_key BLOB NOT NULL,
+        status TEXT NOT NULL,
+        ack_mode INTEGER NOT NULL
       )
   |]
 
@@ -69,11 +71,11 @@ messages =
     CREATE TABLE IF NOT EXISTS messages
       ( message_id INTEGER PRIMARY KEY,
         conn_alias TEXT REFERENCES connections(conn_alias),
-        agent_msg_id INTEGER,
-        timestamp TEXT,
-        message TEXT,
-        direction TEXT,
-        msg_status TEXT
+        agent_msg_id INTEGER NOT NULL,
+        timestamp TEXT NOT NULL,
+        message BLOB NOT NULL,
+        direction TEXT NOT NULL,
+        msg_status TEXT NOT NULL
       )
   |]