diff --git a/libs/core/langchain_core/runnables/config.py b/libs/core/langchain_core/runnables/config.py
index c9e7904a5a..15f2006aab 100644
--- a/libs/core/langchain_core/runnables/config.py
+++ b/libs/core/langchain_core/runnables/config.py
@@ -305,12 +305,12 @@ def merge_configs(*configs: Optional[RunnableConfig]) -> RunnableConfig:
                         base["callbacks"] = mngr
                     else:
                         # base_callbacks is also a manager
-                        base["callbacks"] = base_callbacks.__class__(
+
+                        manager = base_callbacks.__class__(
                             parent_run_id=base_callbacks.parent_run_id
                             or these_callbacks.parent_run_id,
-                            handlers=base_callbacks.handlers + these_callbacks.handlers,
-                            inheritable_handlers=base_callbacks.inheritable_handlers
-                            + these_callbacks.inheritable_handlers,
+                            handlers=[],
+                            inheritable_handlers=[],
                             tags=list(set(base_callbacks.tags + these_callbacks.tags)),
                             inheritable_tags=list(
                                 set(
@@ -323,6 +323,20 @@ def merge_configs(*configs: Optional[RunnableConfig]) -> RunnableConfig:
                                 **these_callbacks.metadata,
                             },
                         )
+
+                        handlers = base_callbacks.handlers + these_callbacks.handlers
+                        inheritable_handlers = (
+                            base_callbacks.inheritable_handlers
+                            + these_callbacks.inheritable_handlers
+                        )
+
+                        for handler in handlers:
+                            manager.add_handler(handler)
+
+                        for handler in inheritable_handlers:
+                            manager.add_handler(handler, inherit=True)
+
+                        base["callbacks"] = manager
             else:
                 base[key] = config[key] or base.get(key)  # type: ignore
     return base
diff --git a/libs/core/tests/unit_tests/runnables/test_runnable_events_v2.py b/libs/core/tests/unit_tests/runnables/test_runnable_events_v2.py
index 88d19f3372..d03bd195c4 100644
--- a/libs/core/tests/unit_tests/runnables/test_runnable_events_v2.py
+++ b/libs/core/tests/unit_tests/runnables/test_runnable_events_v2.py
@@ -1876,3 +1876,34 @@ async def test_runnable_generator() -> None:
             "tags": [],
         },
     ]
+
+
+async def test_with_explicit_config() -> None:
+    """Test astream events with explicit callbacks being passed."""
+    infinite_cycle = cycle([AIMessage(content="hello world", id="ai3")])
+    model = GenericFakeChatModel(messages=infinite_cycle)
+
+    @tool
+    async def say_hello(query: str, callbacks: Callbacks) -> BaseMessage:
+        """Use this tool to look up which items are in the given place."""
+
+        @RunnableLambda
+        def passthrough_to_trigger_issue(x: str) -> str:
+            """Add passthrough to trigger issue."""
+            return x
+
+        chain = passthrough_to_trigger_issue | model.with_config(
+            {"tags": ["hello"], "callbacks": callbacks}
+        )
+
+        return await chain.ainvoke(query)
+
+    events = await _collect_events(
+        say_hello.astream_events("meow", version="v2")  # type: ignore
+    )
+
+    assert [
+        event["data"]["chunk"].content
+        for event in events
+        if event["event"] == "on_chat_model_stream"
+    ] == ["hello", " ", "world"]