diff --git a/src/extensions/photomaker_extension.cpp b/src/extensions/photomaker_extension.cpp
index 78c5cdb9b..48b023f99 100644
--- a/src/extensions/photomaker_extension.cpp
+++ b/src/extensions/photomaker_extension.cpp
@@ -56,7 +56,7 @@ tokenize_photomaker_trigger(FrozenCLIPEmbedderWithCustomWords& clip_conditioner,
                                           true);
     std::vector<bool> class_token_mask;
     for (int i = 0; i < tokens.size(); i++) {
-        class_token_mask.push_back(class_idx + 1 <= i && i < class_idx + 1 + trigger_token_count);
+        class_token_mask.push_back(class_idx >= 0 && class_idx + 1 <= i && i < class_idx + 1 + trigger_token_count);
     }
 
     return std::make_tuple(tokens, weights, class_token_mask);