diff --git a/src/google/adk/agents/llm_agent.py b/src/google/adk/agents/llm_agent.py
index 51205a4d36f..ac2410d08ee 100644
--- a/src/google/adk/agents/llm_agent.py
+++ b/src/google/adk/agents/llm_agent.py
@@ -167,10 +167,17 @@ async def _convert_tool_union_to_tools(
   # other tools.
   # TODO: Remove once the workaround is no longer needed.
   if multiple_tools and isinstance(tool_union, VertexAiSearchTool):
-    from ..tools.discovery_engine_search_tool import DiscoveryEngineSearchTool
-
     vais_tool = tool_union
     if vais_tool.bypass_multi_tools_limit:
+      try:
+        from ..tools.discovery_engine_search_tool import DiscoveryEngineSearchTool
+      except ImportError as e:
+        raise ImportError(
+            'VertexAiSearchTool with bypass_multi_tools_limit=True requires'
+            ' the google-cloud-discoveryengine package. Install it with'
+            ' `pip install google-adk[gcp]`.'
+        ) from e
+
       return [
           DiscoveryEngineSearchTool(
               data_store_id=vais_tool.data_store_id,
diff --git a/tests/unittests/agents/test_llm_agent_fields.py b/tests/unittests/agents/test_llm_agent_fields.py
index 78eb92524f8..0878262dc17 100644
--- a/tests/unittests/agents/test_llm_agent_fields.py
+++ b/tests/unittests/agents/test_llm_agent_fields.py
@@ -595,6 +595,28 @@ async def test_handle_vais_with_other_tools(self):
     assert tools[1].name == 'discovery_engine_search'
     assert tools[1].__class__.__name__ == 'DiscoveryEngineSearchTool'
 
+  async def test_handle_vais_with_other_tools_missing_gcp_extra(self):
+    """Missing google-cloud-discoveryengine raises an actionable error."""
+    agent = LlmAgent(
+        name='test_agent',
+        model='gemini-pro',
+        tools=[
+            self._my_tool,
+            VertexAiSearchTool(
+                data_store_id='test_data_store_id',
+                bypass_multi_tools_limit=True,
+            ),
+        ],
+    )
+    ctx = await _create_readonly_context(agent)
+
+    with mock.patch.dict(
+        'sys.modules',
+        {'google.adk.tools.discovery_engine_search_tool': None},
+    ):
+      with pytest.raises(ImportError, match='google-adk\\[gcp\\]'):
+        await agent.canonical_tools(ctx)
+
   async def test_handle_vais_with_other_tools_no_bypass(self):
     """Test that VertexAiSearchTool is not replaced."""
     agent = LlmAgent(