diff --git a/llama_stack/providers/impls/meta_reference/safety/llama_guard.py b/llama_stack/providers/impls/meta_reference/safety/llama_guard.py
index 19a20a899..a6f450fae 100644
--- a/llama_stack/providers/impls/meta_reference/safety/llama_guard.py
+++ b/llama_stack/providers/impls/meta_reference/safety/llama_guard.py
@@ -170,7 +170,7 @@ class LlamaGuardShield(ShieldBase):
         for i in range(1, len(messages)):
             if messages[i].role == messages[i - 1].role:
                 raise ValueError(
-                    f"Messages must alternate between user and assistant. Message {i} has the same role as message {i-1}"
+                    f"Messages must alternate between user and assistant. Message {i} has the same role as message {i - 1}"
                 )
         return messages