diff --git a/docker/telemetry/docker-compose.grafanacloud.yaml b/docker/telemetry/docker-compose.grafanacloud.yaml
index b78f188d53..ffd7f5fe68 100644
--- a/docker/telemetry/docker-compose.grafanacloud.yaml
+++ b/docker/telemetry/docker-compose.grafanacloud.yaml
@@ -22,6 +22,10 @@ services:
       # Mount the Grafana Cloud collector config over the default path
       # (replaces local-only config for this run; file on disk untouched).
       - ./otel-collector-config.grafanacloud.yaml:/etc/otel-collector-config.yaml:ro
+      # Override the base filelog-storage overlay with the cloud variant. The
+      # collector replaces service.extensions on merge, and the base variant
+      # omits basicauth/grafanacloud, which stops the cloud exporter starting.
+      - ./otel-collector-filestorage.grafanacloud.yaml:/etc/otel-collector-filestorage.yaml:ro
     # Secrets from the env file, injected as container env and
     # resolved by the collector via ${env:...}.
     env_file:
diff --git a/docker/telemetry/otel-collector-filestorage.grafanacloud.yaml b/docker/telemetry/otel-collector-filestorage.grafanacloud.yaml
new file mode 100644
index 0000000000..fe0cfd83e4
--- /dev/null
+++ b/docker/telemetry/otel-collector-filestorage.grafanacloud.yaml
@@ -0,0 +1,26 @@
+# Filelog offset persistence for the Grafana Cloud stack.
+#
+# Same purpose as otel-collector-filestorage.yaml, and needed for the same
+# reason, but it cannot be reused as-is. The collector replaces lists on merge
+# rather than appending, so whichever config is passed last decides
+# service.extensions outright. The base variant repeats the base config's list,
+# [health_check, file_storage/filelog], which drops basicauth/grafanacloud and
+# leaves the cloud exporter unable to resolve its authenticator -- the collector
+# then exits at startup with "authenticator not found" rather than degrading.
+#
+# Applied by docker-compose.grafanacloud.yaml, which mounts it over the base
+# variant so the command line stays unchanged.
+
+extensions:
+  file_storage/filelog:
+    directory: /var/lib/otelcol/file_storage
+    create_directory: true
+
+receivers:
+  filelog:
+    storage: file_storage/filelog
+
+# Must name every extension the cloud config needs, not just this file's own:
+# lists are replaced, so anything omitted here is omitted from the collector.
+service:
+  extensions: [health_check, file_storage/filelog, basicauth/grafanacloud]