diff --git a/app/Main.hs b/app/Main.hs
--- a/app/Main.hs
+++ b/app/Main.hs
@@ -30,6 +30,7 @@
 import Data.Time.Clock (UTCTime, getCurrentTime)
 import Data.Time.Format (formatTime, defaultTimeLocale, rfc822DateFormat)
 import qualified Crypto.Nonce as Nonce
+import Data.Base64.Types (extractBase64)
 import Data.ByteString.Base64.URL (encodeBase64Unpadded)
 import OpenSSL.X509 (writeDerX509)
 import Crypto.Hash.SHA256 (hashlazy)
@@ -56,8 +57,7 @@
 type App = RouteT (ReaderT Context IO)
 
 main :: IO ()
-main = do
-  conn <- SQL.open "gemini-textboard.db"
+main = SQL.withConnection "gemini-textboard.db" $ \conn -> do
   createTables conn
   nonceGen <- Nonce.new
   nonceCache <- Cache.newCache $ Just $ TimeSpec 300 0
@@ -75,10 +75,10 @@
 createTables :: SQL.Connection -> IO ()
 createTables conn = do
   SQL.execute_ conn $ "CREATE TABLE IF NOT EXISTS posts " <>
-    "(id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, " <>
+    -- NOTE: AUTOINCREMENT here is important: it prevents the reuse of deleted ids
+    "(id INTEGER PRIMARY KEY AUTOINCREMENT, " <>
     "parent INTEGER, content TEXT NOT NULL, author TEXT, time TEXT NOT NULL, " <>
-    "FOREIGN KEY(parent) REFERENCES posts(id))"
-  SQL.execute_ conn "CREATE UNIQUE INDEX IF NOT EXISTS post_id_index ON posts (id)"
+    "FOREIGN KEY(parent) REFERENCES posts(id) ON DELETE CASCADE)"
   SQL.execute_ conn "CREATE INDEX IF NOT EXISTS post_parent_index ON posts (parent)"
   SQL.execute_ conn "CREATE INDEX IF NOT EXISTS post_time_index ON posts (time)"
 
@@ -115,10 +115,11 @@
   conn <- db <$> lift ask
   now <- liftIO getCurrentTime
   author <- getAuthor
-  liftIO $ SQL.execute conn
-    "INSERT INTO posts (parent, content, author, time) VALUES (NULL,?,?,?)"
-    (content, author, now)
-  fmap fromIntegral $ liftIO $ SQL.lastInsertRowId conn --TODO non thread safe?
+  liftIO $ SQL.withTransaction conn $ do
+    SQL.execute conn
+      "INSERT INTO posts (parent, content, author, time) VALUES (NULL,?,?,?)"
+      (content, author, now)
+    fromIntegral <$> SQL.lastInsertRowId conn
 
 insertReply :: PostId -> String -> App ()
 insertReply threadId content = do
@@ -154,7 +155,7 @@
     -- Huge hack, but it works reasonably well.
     -- Ideally one should only hash the pk parameters.
     der <- liftIO $ writeDerX509 c
-    pure $ encodeBase64Unpadded $ hashlazy der
+    pure $ extractBase64 $ encodeBase64Unpadded $ hashlazy der
 
 -- Handlers
 -----------
@@ -237,7 +238,7 @@
   pure $ redirect $ fromJust $ parseRelativeReference $ "/thread/" <> show threadId
 
 robotsTxt :: App Response
-robotsTxt = pure $ okGemini $ encodeUtf8
+robotsTxt = pure $ okPlain $ encodeUtf8
   "User-agent: *\n\
   \# Do not crawl submission pages\n\
   \Disallow: /post/\n\
diff --git a/gemini-textboard.cabal b/gemini-textboard.cabal
--- a/gemini-textboard.cabal
+++ b/gemini-textboard.cabal
@@ -1,7 +1,7 @@
 cabal-version:       2.2
 
 name:                gemini-textboard
-version:             0.2.0.1
+version:             0.2.0.2
 synopsis:            A barebones textboard for the Gemini protocol
 -- description:
 homepage:            https://sr.ht/~fgaz/haskell-gemini/
@@ -21,8 +21,7 @@
 executable gemini-textboard
   main-is:             Main.hs
   other-extensions:    OverloadedStrings
-  build-depends:       base ^>=4.12.0.0 || ^>=4.13.0.0 || ^>=4.14.0.0
-                       -- blocked on sqlite-simple || ^>=4.15.0.0
+  build-depends:       base >=4.14 && <4.22
                      , gemini-server ^>=0.3.0.0
                      , gemini-router ^>=0.1.1.0
                      , language-gemini ^>=0.1.0.0
@@ -30,12 +29,12 @@
                      , cache ^>=0.1.3.0
                      , sqlite-simple ^>=0.4.18.0
                      , clock ^>=0.8
-                     , text ^>=1.2.3.2
-                     , time ^>=1.9.3 || ^>=1.10
+                     , text ^>=1.2.3.2 || ^>=2.0 || ^>=2.1
+                     , time ^>=1.9.3 || ^>=1.10 || ^>=1.11 || ^>=1.12 || ^>=1.14
                      , network-uri ^>=2.6.3.0 || ^>=2.7.0.0
-                     , transformers ^>=0.5.6.2
+                     , transformers ^>=0.5.6.2 || ^>=0.6
                      , cryptohash-sha256 ^>=0.11.102
-                     , base64 ^>=0.4.2
+                     , base64 ^>=1.0
                      , HsOpenSSL ^>=0.11.5.1
   hs-source-dirs:      app
   ghc-options:         -Wall -threaded