diff --git a/src/agents/tool.py b/src/agents/tool.py
index 393db09f56..61ba6d2f42 100644
--- a/src/agents/tool.py
+++ b/src/agents/tool.py
@@ -1391,6 +1391,21 @@ def _extract_tool_argument_json_error(error: Exception) -> json.JSONDecodeError
     return _extract_json_decode_error(error)
 
 
+def _is_tool_argument_input_error(error: Exception) -> bool:
+    """Return True when an error represents a non-object JSON input for a function tool.
+
+    Only the non-object case is matched here: schema validation failures share the
+    `Invalid JSON input for tool` prefix and should continue to flow through the
+    regular validation path rather than be reported as JSON parse errors.
+    """
+    if not isinstance(error, ModelBehaviorError):
+        return False
+    text = str(error)
+    return text.startswith("Invalid JSON input for tool") and text.endswith(
+        "expected a JSON object"
+    )
+
+
 def _build_handled_function_tool_error_handler(
     *,
     span_message: str,
@@ -1411,6 +1426,11 @@ def _on_handled_error(
         if json_decode_error is not None and span_message_for_json_decode_error is not None:
             resolved_span_message = span_message_for_json_decode_error
             span_error_detail = str(json_decode_error)
+        elif span_message_for_json_decode_error is not None and _is_tool_argument_input_error(
+            error
+        ):
+            resolved_span_message = span_message_for_json_decode_error
+            span_error_detail = str(error)
         else:
             resolved_span_message = span_message
             span_error_detail = str(error)
@@ -1481,6 +1501,12 @@ def default_tool_error_function(ctx: RunContextWrapper[Any], error: Exception) -
             "Please try again with valid JSON. "
             f"Error: {json_decode_error}"
         )
+    if _is_tool_argument_input_error(error):
+        return (
+            "An error occurred while parsing tool arguments. "
+            "Please try again with valid JSON. "
+            f"Error: {error}"
+        )
     return f"An error occurred while running the tool. Please try again. Error: {str(error)}"
 
 
diff --git a/tests/test_function_tool.py b/tests/test_function_tool.py
index f03996a30e..2f486b5a81 100644
--- a/tests/test_function_tool.py
+++ b/tests/test_function_tool.py
@@ -759,6 +759,57 @@ def echo(value: str) -> str:
         )
 
 
+@pytest.mark.asyncio
+@pytest.mark.parametrize("input_json", ["[]", '"value"', "123", "null", "true"])
+async def test_default_error_function_treats_non_object_input_as_json_error(
+    input_json: str,
+) -> None:
+    def echo(value: str) -> str:
+        return value
+
+    tool = function_tool(echo, name_override="echo_tool")
+
+    result = await tool.on_invoke_tool(
+        ToolContext(
+            None,
+            tool_name="echo_tool",
+            tool_call_id="1",
+            tool_arguments=input_json,
+        ),
+        input_json,
+    )
+
+    assert isinstance(result, str)
+    assert result.startswith("An error occurred while parsing tool arguments.")
+    assert "expected a JSON object" in result
+
+
+@pytest.mark.asyncio
+async def test_default_error_function_does_not_route_schema_validation_as_json_error() -> None:
+    # Schema validation errors share the `Invalid JSON input for tool` prefix
+    # but should continue to flow through the generic error path, not the
+    # "An error occurred while parsing tool arguments" path used for malformed
+    # JSON / non-object inputs.
+    def echo(value: str) -> str:
+        return value
+
+    tool = function_tool(echo, name_override="echo_tool")
+
+    result = await tool.on_invoke_tool(
+        ToolContext(
+            None,
+            tool_name="echo_tool",
+            tool_call_id="1",
+            tool_arguments='{"value": 123}',
+        ),
+        '{"wrong_field": "x"}',
+    )
+
+    assert isinstance(result, str)
+    assert "Invalid JSON input for tool" in result
+    assert not result.startswith("An error occurred while parsing tool arguments.")
+
+
 @pytest.mark.asyncio
 async def test_default_failure_error_function_survives_deepcopy() -> None:
     def boom() -> None: