diff --git a/vllm_omni/diffusion/models/ovis_image/pipeline_ovis_image.py b/vllm_omni/diffusion/models/ovis_image/pipeline_ovis_image.py
index eb62b83b3..8de617dd9 100644
--- a/vllm_omni/diffusion/models/ovis_image/pipeline_ovis_image.py
+++ b/vllm_omni/diffusion/models/ovis_image/pipeline_ovis_image.py
@@ -685,6 +685,7 @@ class OvisImagePipeline(nn.Module, CFGParallelMixin, DiffusionPipelineProfilerMi
 
         negative_text_ids = None
         if do_classifier_free_guidance:
+            negative_prompt = negative_prompt if negative_prompt is not None else ""
             negative_prompt_embeds, negative_text_ids = self.encode_prompt(
                 prompt=negative_prompt,
                 prompt_embeds=negative_prompt_embeds,