diff --git a/lite_bootstrap/bootstrappers/litestar_bootstrapper.py b/lite_bootstrap/bootstrappers/litestar_bootstrapper.py
index e8cefff..a846c53 100644
--- a/lite_bootstrap/bootstrappers/litestar_bootstrapper.py
+++ b/lite_bootstrap/bootstrappers/litestar_bootstrapper.py
@@ -52,6 +52,7 @@
     from litestar.types.asgi_types import ASGIApp, Receive, Scope, Send
     from opentelemetry.instrumentation.asgi import OpenTelemetryMiddleware
     from opentelemetry.trace import TracerProvider
+    from opentelemetry.util.http import parse_excluded_urls
 
 if import_checker.is_opentelemetry_installed:
     from opentelemetry.trace import get_tracer_provider
@@ -99,7 +100,8 @@ def build_litestar_route_details_from_scope(
     class LitestarOpenTelemetryInstrumentationMiddleware(ASGIMiddleware):
         def __init__(self, tracer_provider: "TracerProvider", excluded_urls: set[str]) -> None:
             self._tracer_provider = tracer_provider
-            self._excluded_urls = ",".join(excluded_urls)
+            # OpenTelemetryMiddleware only parses a raw string from 0.56b0; the floor is 0.49b0.
+            self._excluded_urls = parse_excluded_urls(",".join(excluded_urls))
             # WeakKeyDictionary so wrapper apps are evicted when Litestar drops the
             # next_app reference (hot reload, plugin add/remove, AppConfig rebuild).
             # Apps that don't support weak references are simply not cached.
diff --git a/tests/test_litestar_bootstrap.py b/tests/test_litestar_bootstrap.py
index 42a73b1..17689a5 100644
--- a/tests/test_litestar_bootstrap.py
+++ b/tests/test_litestar_bootstrap.py
@@ -532,3 +532,24 @@ def test_second_litestar_bootstrapper_bootstrap_raises(litestar_config: Litestar
             assert client.get(litestar_config.health_checks_path).status_code == status_codes.HTTP_200_OK
     finally:
         first.teardown()
+
+
+def test_litestar_otel_middleware_hands_the_instrumentor_a_parsed_exclude_list() -> None:
+    """INVARIANT: `excluded_urls` reaches OpenTelemetryMiddleware parsed, never as a raw string.
+
+    `OpenTelemetryMiddleware` only learned to parse a string itself in
+    opentelemetry-instrumentation 0.56b0. The declared floor is 0.49b0, where a string reaches
+    `self.excluded_urls.url_disabled(url)` and raises `AttributeError` on every request, so a
+    Litestar service with OpenTelemetry returns 500 for everything.
+    """
+    middleware = LitestarOpenTelemetryInstrumentationMiddleware(
+        tracer_provider=TracerProvider(),
+        excluded_urls={"/custom-metrics"},
+    )
+
+    excluded_urls = middleware._excluded_urls  # noqa: SLF001
+    assert not isinstance(excluded_urls, str)
+    # Matched against the URL the middleware builds from `scope["path"]`, which Litestar has
+    # already normalized; see #248 for the trailing-slash entries that therefore never match.
+    assert excluded_urls.url_disabled("http://test/custom-metrics")
+    assert not excluded_urls.url_disabled("http://test/items/1")