diff --git a/backends/native/examples/hf_llm/runtime/LlmRunner.cpp b/backends/native/examples/hf_llm/runtime/LlmRunner.cpp
index 7e8df20df1a..c7cfce656a8 100644
--- a/backends/native/examples/hf_llm/runtime/LlmRunner.cpp
+++ b/backends/native/examples/hf_llm/runtime/LlmRunner.cpp
@@ -349,14 +349,15 @@ struct Generation {
 
 // Prefills `prompt_tokens` from `start_position` in calls of at most
 // `max_chunk` tokens, then decodes one token per call until `limit` tokens or
-// an EOS, streaming the text to stdout. With --warmup_prefill it prefills the
-// prompt once beforehand, then clears `offgraph_cache` if there is one.
+// an EOS, streaming the text to stdout unless `tokenizer` is null. With
+// --warmup_prefill it prefills the prompt once beforehand, then clears
+// `offgraph_cache` if there is one.
 Generation generate(
     ptn::EngineExecutable& executable,
     size_t logits_output,
     bool per_token_positions,
     size_t max_chunk,
-    ::tokenizers::Tiktoken& tokenizer,
+    const ::tokenizers::Tiktoken* tokenizer,
     const std::vector<uint64_t>& prompt_tokens,
     int64_t start_position,
     size_t limit,
@@ -488,19 +489,21 @@ Generation generate(
   size_t generated = 0;
   std::vector<uint64_t> generated_ids;
   uint64_t previous_token = prompt_tokens.back();
-  if (!FLAGS_interactive) {
+  if (tokenizer != nullptr && !FLAGS_interactive) {
     std::printf("text:      ");
   }
   std::fflush(stdout);
   while (generated < limit && !eos_ids.contains(next_token)) {
-    auto decoded = tokenizer.decode(previous_token, next_token);
-    if (!decoded.ok()) {
-      throw std::runtime_error(
-          "failed to decode token: tokenizer error " +
-          std::to_string(static_cast<uint32_t>(decoded.error())));
+    if (tokenizer != nullptr) {
+      auto decoded = tokenizer->decode(previous_token, next_token);
+      if (!decoded.ok()) {
+        throw std::runtime_error(
+            "failed to decode token: tokenizer error " +
+            std::to_string(static_cast<uint32_t>(decoded.error())));
+      }
+      std::printf("%s", decoded.get().c_str());
+      std::fflush(stdout);
     }
-    std::printf("%s", decoded.get().c_str());
-    std::fflush(stdout);
     previous_token = next_token;
     if (FLAGS_print_token_ids) {
       generated_ids.push_back(next_token);
@@ -517,7 +520,9 @@ Generation generate(
       ++generation.decode_steps;
     }
   }
-  std::printf("\n");
+  if (tokenizer != nullptr) {
+    std::printf("\n");
+  }
   generation.unfed_token = next_token;
   generation.ended_on_eos = eos_ids.contains(next_token);
   if (FLAGS_print_token_ids) {
@@ -805,7 +810,8 @@ int run_llm(
             logits_output,
             per_token_positions,
             static_cast<size_t>(token_shape[1]),
-            *tokenizer,
+            // The sample's tokens need not be in --tokenizer's vocabulary.
+            nullptr,
             prompt,
             0,
             calls.size(),
@@ -895,7 +901,7 @@ int run_llm(
             logits_output,
             per_token_positions,
             static_cast<size_t>(token_shape[1]),
-            *tokenizer,
+            tokenizer.get(),
             tokens,
             position,
             limit,
@@ -921,7 +927,7 @@ int run_llm(
         logits_output,
         per_token_positions,
         static_cast<size_t>(token_shape[1]),
-        *tokenizer,
+        tokenizer.get(),
         prompt_tokens,
         0,
         limit,