diff --git a/src/backend/src/api/APIError.js b/src/backend/src/api/APIError.js
index a0b958055..3f23dc404 100644
--- a/src/backend/src/api/APIError.js
+++ b/src/backend/src/api/APIError.js
@@ -509,6 +509,12 @@ module.exports = class APIError {
             status: 400,
             message: ({ engine, valid_engines }) => `Invalid engine: ${quot(engine)}. Valid engines are: ${valid_engines.map(quot).join(', ')}.`,
         },
+        
+        // Abuse prevention
+        'moderation_failed': {
+            status: 422,
+            message: `Content moderation failed`,
+        },
     };
 
     /**
diff --git a/src/backend/src/modules/puterai/AIChatService.js b/src/backend/src/modules/puterai/AIChatService.js
index 9edc00c8f..5ed9db4cd 100644
--- a/src/backend/src/modules/puterai/AIChatService.js
+++ b/src/backend/src/modules/puterai/AIChatService.js
@@ -324,6 +324,7 @@ class AIChatService extends BaseService {
 
                 if ( ! test_mode && ! await this.moderate(parameters) ) {
                     test_mode = true;
+                    throw APIError.create('moderation_failed');
                 }
 
                 if ( ! test_mode ) {
@@ -622,6 +623,7 @@ class AIChatService extends BaseService {
     * Returns true if OpenAI service is unavailable or all messages pass moderation.
     */
     async moderate({ messages }) {
+        if ( process.env.TEST_MODERATION_FAILURE ) return false;
         for ( const msg of messages ) {
             const texts = [];