diff --git a/vllm/inputs/preprocess.py b/vllm/inputs/preprocess.py
index 53f89996f0fe9..035e84cc0633d 100644
--- a/vllm/inputs/preprocess.py
+++ b/vllm/inputs/preprocess.py
@@ -260,6 +260,9 @@ def _process_multimodal(
         mm_processor = self.mm_registry.create_processor(
             self.model_config, tokenizer)
 
+        if isinstance(prompt, list):
+            prompt = tokenizer.decode(prompt)
+
         if mm_processor_kwargs is None:
             mm_processor_kwargs = {}