diff --git a/custom_components/openai_compatible/config_flow.py b/custom_components/openai_compatible/config_flow.py
index cd91d94..1bf7525 100644
--- a/custom_components/openai_compatible/config_flow.py
+++ b/custom_components/openai_compatible/config_flow.py
@@ -708,9 +708,11 @@ class OpenAISubentryFlowHandler(ConfigSubentryFlow):
             try:
                 response = await client.responses.create(
                     model=self.options.get(CONF_CHAT_MODEL, RECOMMENDED_CHAT_MODEL),
+                    # A user message, not a system one: endpoints in front of
+                    # Anthropic models reject a request without user content.
                     input=[
                         {
-                            "role": "system",
+                            "role": "user",
                             "content": "Where are the following coordinates located: "
                             f"({zone_home.attributes[EntityStateAttribute.LATITUDE]},"
                             f" {zone_home.attributes[EntityStateAttribute.LONGITUDE]})?",
diff --git a/custom_components/openai_compatible/entity.py b/custom_components/openai_compatible/entity.py
index 2f86269..bfbf344 100644
--- a/custom_components/openai_compatible/entity.py
+++ b/custom_components/openai_compatible/entity.py
@@ -560,12 +560,20 @@ class OpenAIBaseLLMEntity(Entity):
                 ),
             )
             if options.get(CONF_WEB_SEARCH_USER_LOCATION):
+                # Leave out unknown fields: some endpoints reject empty strings,
+                # and the location lookup may have found no city or region.
+                location = {
+                    key: value
+                    for key, option in (
+                        ("city", CONF_WEB_SEARCH_CITY),
+                        ("region", CONF_WEB_SEARCH_REGION),
+                        ("country", CONF_WEB_SEARCH_COUNTRY),
+                        ("timezone", CONF_WEB_SEARCH_TIMEZONE),
+                    )
+                    if (value := options.get(option))
+                }
                 web_search["user_location"] = UserLocation(
-                    type="approximate",
-                    city=options.get(CONF_WEB_SEARCH_CITY, ""),
-                    region=options.get(CONF_WEB_SEARCH_REGION, ""),
-                    country=options.get(CONF_WEB_SEARCH_COUNTRY, ""),
-                    timezone=options.get(CONF_WEB_SEARCH_TIMEZONE, ""),
+                    type="approximate", **location
                 )
             if not options.get(
                 CONF_WEB_SEARCH_INLINE_CITATIONS,
diff --git a/tests/test_config_flow.py b/tests/test_config_flow.py
index 4bd1ffc..949c6db 100644
--- a/tests/test_config_flow.py
+++ b/tests/test_config_flow.py
@@ -1334,6 +1334,7 @@ async def test_subentry_web_search_user_location_lookup_fails(
         )
         await hass.async_block_till_done()
     assert mock_create.call_args.kwargs["model"] == "claude-sonnet-5-5"
+    assert mock_create.call_args.kwargs["input"][0]["role"] == "user"
     assert subentry_flow["type"] is FlowResultType.ABORT
     assert subentry_flow["reason"] == "reconfigure_successful"
     assert CONF_WEB_SEARCH_CITY not in subentry.data
diff --git a/tests/test_entity.py b/tests/test_entity.py
index c3b1673..7a8a718 100644
--- a/tests/test_entity.py
+++ b/tests/test_entity.py
@@ -3,14 +3,21 @@
 from unittest.mock import MagicMock
 
 from homeassistant.components import conversation
+from homeassistant.core import Context
 from homeassistant.helpers import llm
 
+from custom_components.openai_compatible.const import (
+    CONF_WEB_SEARCH,
+    CONF_WEB_SEARCH_COUNTRY,
+    CONF_WEB_SEARCH_TIMEZONE,
+    CONF_WEB_SEARCH_USER_LOCATION,
+)
 from custom_components.openai_compatible.entity import (
     _convert_content_to_param,
     _transform_stream,
 )
 
-from . import create_function_tool_call_item
+from . import create_function_tool_call_item, create_message_item
 
 
 async def _stream(events):
@@ -90,3 +97,41 @@ def test_web_search_not_replayed() -> None:
     ]
     assert messages[1]["content"] == "It ended 2 to 2."
     assert messages[2]["call_id"] == "call_1"
+
+
+async def test_web_search_location_leaves_out_empty_fields(
+    hass, mock_config_entry, mock_init_component, mock_create_stream
+) -> None:
+    """Test unknown location fields are left out of the web search tool.
+
+    A failed location lookup stores no city or region; endpoints in front of
+    Anthropic models reject empty strings there.
+    """
+    subentry = next(iter(mock_config_entry.subentries.values()))
+    hass.config_entries.async_update_subentry(
+        mock_config_entry,
+        subentry,
+        data={
+            **subentry.data,
+            CONF_WEB_SEARCH: True,
+            CONF_WEB_SEARCH_USER_LOCATION: True,
+            CONF_WEB_SEARCH_COUNTRY: "DE",
+            CONF_WEB_SEARCH_TIMEZONE: "Europe/Berlin",
+        },
+    )
+    await hass.config_entries.async_reload(mock_config_entry.entry_id)
+    mock_create_stream.return_value = [
+        create_message_item(id="msg_A", text="Hi", output_index=0)
+    ]
+
+    await conversation.async_converse(
+        hass, "hello", None, Context(), agent_id="conversation.openai_conversation"
+    )
+
+    tools = mock_create_stream.mock_calls[0][2]["tools"]
+    web_search = next(tool for tool in tools if tool["type"] == "web_search")
+    assert web_search["user_location"] == {
+        "type": "approximate",
+        "country": "DE",
+        "timezone": "Europe/Berlin",
+    }