diff --git a/src/lib/moderation/queries.ts b/src/lib/moderation/queries.ts
index 7341d750..7276476d 100644
--- a/src/lib/moderation/queries.ts
+++ b/src/lib/moderation/queries.ts
@@ -137,8 +137,9 @@ export function buildSubmissionQuery(
   // Admins see all submissions
   if (!isAdmin && !isSuperuser) {
     const now = new Date().toISOString();
+    // Fixed: Add null check for locked_until to prevent 400 error
     query = query.or(
-      `assigned_to.is.null,locked_until.lt.${now},assigned_to.eq.${userId}`
+      `assigned_to.is.null,and(locked_until.not.is.null,locked_until.lt.${now}),assigned_to.eq.${userId}`
     );
   }
 
@@ -189,8 +190,9 @@ export function buildCountQuery(
 
   if (!isAdmin && !isSuperuser) {
     const now = new Date().toISOString();
+    // Fixed: Add null check for locked_until to prevent 400 error
     countQuery = countQuery.or(
-      `assigned_to.is.null,locked_until.lt.${now},assigned_to.eq.${userId}`
+      `assigned_to.is.null,and(locked_until.not.is.null,locked_until.lt.${now}),assigned_to.eq.${userId}`
     );
   }