diff --git a/libs/core/langchain_core/utils/json_schema.py b/libs/core/langchain_core/utils/json_schema.py
index 3368f83813..be5c8e25ba 100644
--- a/libs/core/langchain_core/utils/json_schema.py
+++ b/libs/core/langchain_core/utils/json_schema.py
@@ -13,10 +13,12 @@ def _retrieve_ref(path: str, schema: dict) -> dict:
         )
     out = schema
     for component in components[1:]:
-        if component.isdigit():
+        if component in out:
+            out = out[component]
+        elif component.isdigit() and int(component) in out:
             out = out[int(component)]
         else:
-            out = out[component]
+            raise KeyError(f"Reference '{path}' not found.")
     return deepcopy(out)
 
 
diff --git a/libs/core/tests/unit_tests/utils/test_json_schema.py b/libs/core/tests/unit_tests/utils/test_json_schema.py
index 44ad61609b..cb2add7476 100644
--- a/libs/core/tests/unit_tests/utils/test_json_schema.py
+++ b/libs/core/tests/unit_tests/utils/test_json_schema.py
@@ -183,6 +183,38 @@ def test_dereference_refs_integer_ref() -> None:
     assert actual == expected
 
 
+def test_dereference_refs_string_ref() -> None:
+    schema = {
+        "type": "object",
+        "properties": {
+            "error_400": {"$ref": "#/$defs/400"},
+        },
+        "$defs": {
+            "400": {
+                "type": "object",
+                "properties": {"description": "Bad Request"},
+            },
+        },
+    }
+    expected = {
+        "type": "object",
+        "properties": {
+            "error_400": {
+                "type": "object",
+                "properties": {"description": "Bad Request"},
+            },
+        },
+        "$defs": {
+            "400": {
+                "type": "object",
+                "properties": {"description": "Bad Request"},
+            },
+        },
+    }
+    actual = dereference_refs(schema)
+    assert actual == expected
+
+
 def test_dereference_refs_cyclical_refs() -> None:
     schema = {
         "type": "object",