diff --git a/server/repos.js b/server/repos.js
index baf2195..319f31f 100644
--- a/server/repos.js
+++ b/server/repos.js
@@ -213,13 +213,17 @@ const messages = {
   // Full 1:1 (DM) thread between two users (both directions). Take the NEWEST `limit` messages
   // (inner DESC), then present them oldest-first. The old plain "ASC LIMIT" returned the OLDEST 300
   // and silently dropped everything newer once a thread passed 300 — so new messages "disappeared".
-  thread: (teamId, a, b, limit = 500, before = null) =>
-    db.prepare(`SELECT * FROM (
+  // The `before` cursor is added CONDITIONALLY (not as `? IS NULL OR …`): an all-NULL param has no type
+  // for Postgres to infer. The subquery also needs an alias (`t`) — Postgres requires it. Both portable.
+  thread: (teamId, a, b, limit = 500, before = null) => {
+    const cond = before != null ? ' AND created_at < ?' : '';
+    const args = before != null ? [teamId, a, b, b, a, before, limit] : [teamId, a, b, b, a, limit];
+    return db.prepare(`SELECT * FROM (
         SELECT * FROM messages WHERE team_id=? AND conversation_id IS NULL
-          AND ((sender_id=? AND recipient_id=?) OR (sender_id=? AND recipient_id=?))
-          AND (? IS NULL OR created_at < ?)
+          AND ((sender_id=? AND recipient_id=?) OR (sender_id=? AND recipient_id=?))${cond}
           ORDER BY created_at DESC LIMIT ?
-      ) ORDER BY created_at ASC`).all(teamId, a, b, b, a, before, before, limit),
+      ) t ORDER BY created_at ASC`).all(...args);
+  },
   // Full-thread search (ALL messages, not just the loaded window). `like` is the escaped LIKE pattern.
   searchThread: (teamId, a, b, like, limit = 300) =>
     db.prepare(`SELECT id, created_at, sender_id FROM messages WHERE team_id=? AND conversation_id IS NULL
@@ -233,10 +237,13 @@ const messages = {
     db.prepare('SELECT * FROM messages WHERE team_id=? AND conversation_id IS NULL AND (sender_id=? OR recipient_id=?) ORDER BY created_at DESC LIMIT ?')
       .all(teamId, userId, userId, limit),
   // Group conversation helpers.
-  threadByConversation: (conversationId, limit = 500, before = null) =>
-    db.prepare(`SELECT * FROM (
-        SELECT * FROM messages WHERE conversation_id=? AND (? IS NULL OR created_at < ?) ORDER BY created_at DESC LIMIT ?
-      ) ORDER BY created_at ASC`).all(conversationId, before, before, limit),
+  threadByConversation: (conversationId, limit = 500, before = null) => {
+    const cond = before != null ? ' AND created_at < ?' : '';
+    const args = before != null ? [conversationId, before, limit] : [conversationId, limit];
+    return db.prepare(`SELECT * FROM (
+        SELECT * FROM messages WHERE conversation_id=?${cond} ORDER BY created_at DESC LIMIT ?
+      ) t ORDER BY created_at ASC`).all(...args);
+  },
   searchConversation: (conversationId, like, limit = 300) =>
     db.prepare(`SELECT id, created_at, sender_id FROM messages WHERE conversation_id=? AND deleted=0
         AND body LIKE ? ESCAPE '\\' ORDER BY created_at ASC LIMIT ?`).all(conversationId, like, limit),