diff --git a/llama-index-core/llama_index/core/base/llms/types.py b/llama-index-core/llama_index/core/base/llms/types.py
index 66ad45b08de361..fb19cb58892bd4 100644
--- a/llama-index-core/llama_index/core/base/llms/types.py
+++ b/llama-index-core/llama_index/core/base/llms/types.py
@@ -14,6 +14,7 @@ class MessageRole(str, Enum):
     FUNCTION = "function"
     TOOL = "tool"
     CHATBOT = "chatbot"
+    MODEL = "model"
 
 
 # ===== Generic Model Input - Chat =====
diff --git a/llama-index-integrations/llms/llama-index-llms-gemini/llama_index/llms/gemini/utils.py b/llama-index-integrations/llms/llama-index-llms-gemini/llama_index/llms/gemini/utils.py
index 8bc01a53c076bf..44415e6a2bec66 100644
--- a/llama-index-integrations/llms/llama-index-llms-gemini/llama_index/llms/gemini/utils.py
+++ b/llama-index-integrations/llms/llama-index-llms-gemini/llama_index/llms/gemini/utils.py
@@ -3,11 +3,12 @@
 import google.ai.generativelanguage as glm
 import google.generativeai as genai
 import PIL
-from llama_index.core.base.llms.types import MessageRole
+
 from llama_index.core.base.llms.types import (
     ChatMessage,
     ChatResponse,
     CompletionResponse,
+    MessageRole,
 )
 
 ROLES_TO_GEMINI = {
@@ -105,7 +106,7 @@ def merge_neighboring_same_role_messages(
 
         # Create a new ChatMessage or similar object with merged content
         merged_message = ChatMessage(
-            role=current_message.role,
+            role=ROLES_TO_GEMINI[current_message.role],
             content="\n".join([str(msg_content) for msg_content in merged_content]),
             additional_kwargs=current_message.additional_kwargs,
         )
diff --git a/llama-index-integrations/llms/llama-index-llms-vertex/llama_index/llms/vertex/utils.py b/llama-index-integrations/llms/llama-index-llms-vertex/llama_index/llms/vertex/utils.py
index c9f7bb2f9e97da..69c2ec481a3d2f 100644
--- a/llama-index-integrations/llms/llama-index-llms-vertex/llama_index/llms/vertex/utils.py
+++ b/llama-index-integrations/llms/llama-index-llms-vertex/llama_index/llms/vertex/utils.py
@@ -6,7 +6,6 @@
 
 import google.api_core
 import vertexai
-from llama_index.core.base.llms.types import ChatMessage, MessageRole
 from tenacity import (
     before_sleep_log,
     retry,
@@ -14,12 +13,10 @@
     stop_after_attempt,
     wait_exponential,
 )
-from vertexai.language_models import (
-    ChatMessage as VertexChatMessage,
-)
-from vertexai.language_models import (
-    InputOutputTextPair,
-)
+from vertexai.language_models import ChatMessage as VertexChatMessage
+from vertexai.language_models import InputOutputTextPair
+
+from llama_index.core.base.llms.types import ChatMessage, MessageRole
 
 CHAT_MODELS = ["chat-bison", "chat-bison-32k", "chat-bison@001"]
 TEXT_MODELS = ["text-bison", "text-bison-32k", "text-bison@001"]
@@ -171,7 +168,7 @@ def _parse_chat_history(history: Any, is_gemini: bool) -> Any:
             if is_gemini:
                 raise ValueError("Gemini model don't support system messages")
             context = message.content
-        elif message.role == MessageRole.ASSISTANT or message.role == MessageRole.USER:
+        elif message.role == MessageRole.MODEL or message.role == MessageRole.USER:
             if is_gemini:
                 from llama_index.llms.vertex.gemini_utils import (
                     convert_chat_message_to_gemini_content,
@@ -185,12 +182,12 @@ def _parse_chat_history(history: Any, is_gemini: bool) -> Any:
             else:
                 vertex_message = VertexChatMessage(
                     content=message.content,
-                    author="bot" if message.role == MessageRole.ASSISTANT else "user",
+                    author=("bot" if message.role == MessageRole.MODEL else "user"),
                 )
                 vertex_messages.append(vertex_message)
         else:
             raise ValueError(
-                f"Unexpected message with type {type(message)} at the position {i}."
+                f"Unexpected message with role {message.role} at the position {i}."
             )
     if len(vertex_messages) % 2 != 0:
         raise ValueError("total no of messages should be even")