diff --git a/neuron-explainer/neuron_explainer/explanations/prompt_builder.py b/neuron-explainer/neuron_explainer/explanations/prompt_builder.py
index 3782940..8776e7f 100644
--- a/neuron-explainer/neuron_explainer/explanations/prompt_builder.py
+++ b/neuron-explainer/neuron_explainer/explanations/prompt_builder.py
@@ -49,8 +49,13 @@ class Role(str, Enum):
 class PromptBuilder:
     """Class for accumulating components of a prompt and then formatting them into an output."""
 
-    def __init__(self) -> None:
+
+    def __init__(self, allow_extra_system_messages: bool = False) -> None:
+        """The `allow_extra_system_messages` instance variable allows the caller to specify that the prompt
+        should be allowed to contain system messages after the very first one."""
+
         self._messages: list[HarmonyMessage] = []
+        self._allow_extra_system_messages = allow_extra_system_messages
 
     def add_message(self, role: Role, message: str) -> None:
         self._messages.append(HarmonyMessage(role=role, content=message))
@@ -93,7 +98,7 @@ def build(
         for message in messages:
             role = message["role"]
             assert role == expected_next_role or (
-                allow_extra_system_messages and role == Role.SYSTEM
+                (self._allow_extra_system_messages or allow_extra_system_messages) and role == Role.SYSTEM
             ), f"Expected message from {expected_next_role} but got message from {role}"
             if role == Role.SYSTEM:
                 expected_next_role = Role.USER