diff --git a/pydantic_ai_slim/pydantic_ai/_output.py b/pydantic_ai_slim/pydantic_ai/_output.py
index cc05b1889..0b52ad8cd 100644
--- a/pydantic_ai_slim/pydantic_ai/_output.py
+++ b/pydantic_ai_slim/pydantic_ai/_output.py
@@ -2,6 +2,7 @@
 
 import inspect
 import json
+import re
 from abc import ABC, abstractmethod
 from collections.abc import Awaitable, Callable, Sequence
 from dataclasses import dataclass, field
@@ -70,6 +71,7 @@
 
 DEFAULT_OUTPUT_TOOL_NAME = 'final_result'
 DEFAULT_OUTPUT_TOOL_DESCRIPTION = 'The final response which ends this conversation'
+OUTPUT_TOOL_NAME_SANITIZER = re.compile(r'[^a-z0-9-_]')
 
 
 async def execute_traced_output_function(
@@ -997,7 +999,9 @@ def build(
             if name is None:
                 name = default_name
                 if multiple:
-                    name += f'_{object_def.name}'
+                    # strip unsupported characters like "[" and "]" from generic class names
+                    safe_name = OUTPUT_TOOL_NAME_SANITIZER.sub('', object_def.name or '')
+                    name += f'_{safe_name}'
 
             i = 1
             original_name = name