diff --git a/packages/ragbits-core/src/ragbits/core/prompt/prompt.py b/packages/ragbits-core/src/ragbits/core/prompt/prompt.py
index 443fb280..75b3c093 100644
--- a/packages/ragbits-core/src/ragbits/core/prompt/prompt.py
+++ b/packages/ragbits-core/src/ragbits/core/prompt/prompt.py
@@ -22,7 +22,7 @@ class Prompt(Generic[InputT, OutputT], BasePromptWithParser[OutputT], metaclass=
 
     system_prompt: Optional[str] = None
     user_prompt: str
-    additional_messages: ChatFormat = []
+    additional_messages: Optional[ChatFormat] = None
 
     # function that parses the response from the LLM to specific output type
     # if not provided, the class tries to set it automatically based on the output type
@@ -125,10 +125,13 @@ def chat(self) -> ChatFormat:
         Returns:
             ChatFormat: A list of dictionaries, each containing the role and content of a message.
         """
-        return [
+        chat = [
             *([{"role": "system", "content": self.system_message}] if self.system_message is not None else []),
             {"role": "user", "content": self.user_message},
-        ] + self.additional_messages
+        ]
+        if self.additional_messages:
+            chat.extend(self.additional_messages)
+        return chat
 
     def add_user_message(self, message: str) -> "Prompt[InputT, OutputT]":
         """
@@ -140,6 +143,8 @@ def add_user_message(self, message: str) -> "Prompt[InputT, OutputT]":
         Returns:
             Prompt[InputT, OutputT]: The current prompt instance in order to allow chaining.
         """
+        if self.additional_messages is None:
+            self.additional_messages = []
         self.additional_messages.append({"role": "user", "content": message})
         return self
 
@@ -153,6 +158,8 @@ def add_assistant_message(self, message: str) -> "Prompt[InputT, OutputT]":
         Returns:
             Prompt[InputT, OutputT]: The current prompt instance in order to allow chaining.
         """
+        if self.additional_messages is None:
+            self.additional_messages = []
         self.additional_messages.append({"role": "assistant", "content": message})
         return self
 
diff --git a/packages/ragbits-core/tests/unit/prompts/test_prompt.py b/packages/ragbits-core/tests/unit/prompts/test_prompt.py
index f0e00ebf..557849f0 100644
--- a/packages/ragbits-core/tests/unit/prompts/test_prompt.py
+++ b/packages/ragbits-core/tests/unit/prompts/test_prompt.py
@@ -218,3 +218,36 @@ class TestPrompt(Prompt[_PromptInput, str]):  # pylint: disable=unused-variable
         {"role": "system", "content": "You are a song generator for a adult named John."},
         {"role": "user", "content": "Theme for the song is pop."},
     ]
+
+
+def test_two_instances_do_not_share_additional_messages():
+    """
+    Test that two instances of a prompt do not share additional messages.
+    """
+
+    class TestPrompt(Prompt[_PromptInput, str]):  # pylint: disable=unused-variable
+        """A test prompt"""
+
+        system_prompt = """
+        You are a song generator for a {% if age > 18 %}adult{% else %}child{% endif %} named {{ name }}.
+        """
+        user_prompt = "Theme for the song is {{ theme }}."
+
+    prompt1 = TestPrompt(_PromptInput(name="John", age=15, theme="pop"))
+    prompt1.add_assistant_message("It's a really catchy tune.").add_user_message("I like it.")
+
+    prompt2 = TestPrompt(_PromptInput(name="Alice", age=30, theme="rock"))
+    prompt2.add_assistant_message("It's a nice tune.")
+
+    assert prompt1.chat == [
+        {"role": "system", "content": "You are a song generator for a child named John."},
+        {"role": "user", "content": "Theme for the song is pop."},
+        {"role": "assistant", "content": "It's a really catchy tune."},
+        {"role": "user", "content": "I like it."},
+    ]
+
+    assert prompt2.chat == [
+        {"role": "system", "content": "You are a song generator for a adult named Alice."},
+        {"role": "user", "content": "Theme for the song is rock."},
+        {"role": "assistant", "content": "It's a nice tune."},
+    ]