diff --git a/libs/partners/anthropic/langchain_anthropic/chat_models.py b/libs/partners/anthropic/langchain_anthropic/chat_models.py
index 251afb015c5..dd55d4062c6 100644
--- a/libs/partners/anthropic/langchain_anthropic/chat_models.py
+++ b/libs/partners/anthropic/langchain_anthropic/chat_models.py
@@ -118,9 +118,13 @@ def _merge_messages(
     for curr in messages:
         curr = curr.model_copy(deep=True)
         if isinstance(curr, ToolMessage):
-            if isinstance(curr.content, list) and all(
-                isinstance(block, dict) and block.get("type") == "tool_result"
-                for block in curr.content
+            if (
+                isinstance(curr.content, list)
+                and curr.content
+                and all(
+                    isinstance(block, dict) and block.get("type") == "tool_result"
+                    for block in curr.content
+                )
             ):
                 curr = HumanMessage(curr.content)  # type: ignore[misc]
             else:
diff --git a/libs/partners/anthropic/tests/unit_tests/test_chat_models.py b/libs/partners/anthropic/tests/unit_tests/test_chat_models.py
index 90906edf547..fd84fd338b1 100644
--- a/libs/partners/anthropic/tests/unit_tests/test_chat_models.py
+++ b/libs/partners/anthropic/tests/unit_tests/test_chat_models.py
@@ -162,6 +162,13 @@ def test__merge_messages() -> None:
                     "text": None,
                     "name": "blah",
                 },
+                {
+                    "tool_input": {"a": "c"},
+                    "type": "tool_use",
+                    "id": "3",
+                    "text": None,
+                    "name": "blah",
+                },
             ]
         ),
         ToolMessage("buz output", tool_call_id="1", status="error"),  # type: ignore[misc]
@@ -178,6 +185,7 @@ def test__merge_messages() -> None:
             ],
             tool_call_id="2",
         ),  # type: ignore[misc]
+        ToolMessage([], tool_call_id="3"),  # type: ignore[misc]
         HumanMessage("next thing"),  # type: ignore[misc]
     ]
     expected = [
@@ -201,6 +209,13 @@ def test__merge_messages() -> None:
                     "text": None,
                     "name": "blah",
                 },
+                {
+                    "tool_input": {"a": "c"},
+                    "type": "tool_use",
+                    "id": "3",
+                    "text": None,
+                    "name": "blah",
+                },
             ]
         ),
         HumanMessage(  # type: ignore[misc]
@@ -226,6 +241,12 @@ def test__merge_messages() -> None:
                     "tool_use_id": "2",
                     "is_error": False,
                 },
+                {
+                    "type": "tool_result",
+                    "content": [],
+                    "tool_use_id": "3",
+                    "is_error": False,
+                },
                 {"type": "text", "text": "next thing"},
             ]
         ),