diff --git a/src/google/adk/tools/base_toolset.py b/src/google/adk/tools/base_toolset.py
index 25f0d6a2a2..34c022e999 100644
--- a/src/google/adk/tools/base_toolset.py
+++ b/src/google/adk/tools/base_toolset.py
@@ -80,8 +80,7 @@ def __init__(
     """
     self.tool_filter = tool_filter
     self.tool_name_prefix = tool_name_prefix
-    self._cached_invocation_id: Optional[str] = None
-    self._cached_prefixed_tools: Optional[list[BaseTool]] = None
+    self._cached_prefixed_tools: dict[Optional[str], list[BaseTool]] = {}
     self._use_invocation_cache = True
 
   @abstractmethod
@@ -119,16 +118,14 @@ async def get_tools_with_prefix(
 
     if (
         self._use_invocation_cache
-        and self._cached_prefixed_tools is not None
-        and self._cached_invocation_id == invocation_id
+        and invocation_id in self._cached_prefixed_tools
     ):
-      return self._cached_prefixed_tools
+      return self._cached_prefixed_tools[invocation_id]
 
     tools = await self.get_tools(readonly_context)
 
     if not self.tool_name_prefix:
-      self._cached_invocation_id = invocation_id
-      self._cached_prefixed_tools = tools
+      self._cached_prefixed_tools[invocation_id] = tools
       return tools
 
     prefix = self.tool_name_prefix
@@ -161,8 +158,7 @@ def _get_prefixed_declaration():
       tool_copy._get_declaration = _create_prefixed_declaration()
       prefixed_tools.append(tool_copy)
 
-    self._cached_invocation_id = invocation_id
-    self._cached_prefixed_tools = prefixed_tools
+    self._cached_prefixed_tools[invocation_id] = prefixed_tools
     return prefixed_tools
 
   async def close(self) -> None:
@@ -174,6 +170,7 @@ async def close(self) -> None:
       should ensure that any open connections, files, or other managed
       resources are properly released to prevent leaks.
     """
+    self._cached_prefixed_tools.clear()
 
   @classmethod
   def from_config(
diff --git a/tests/unittests/tools/test_base_toolset.py b/tests/unittests/tools/test_base_toolset.py
index cdb7808db7..9b89e570dd 100644
--- a/tests/unittests/tools/test_base_toolset.py
+++ b/tests/unittests/tools/test_base_toolset.py
@@ -48,7 +48,7 @@ async def get_tools(
     return self._tools
 
   async def close(self) -> None:
-    pass
+    await super().close()
 
 
 @pytest.mark.asyncio
@@ -439,6 +439,19 @@ async def test_get_tools_with_prefix_caching():
   assert tools3 is not tools1  # Should be a new list instance
   assert tools3[0].name == 'test_tool1'
 
+  # Fourth call with first invocation_id again (should hit cache)
+  tools1_again = await toolset.get_tools_with_prefix(
+      readonly_context=readonly_context1
+  )
+  assert tools1_again is tools1
+
+  # Test close() clears the cache
+  await toolset.close()
+  tools1_after_close = await toolset.get_tools_with_prefix(
+      readonly_context=readonly_context1
+  )
+  assert tools1_after_close is not tools1
+
   # Test disabling caching
   toolset._use_invocation_cache = False
   tools4 = await toolset.get_tools_with_prefix(