diff --git a/CHANGELOG.md b/CHANGELOG.md
index 86c6aed2..bf687dd6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -20,6 +20,7 @@
 * [CHANGE] Removed `CortexCacheRequestErrors` alert. This alert was not working because the legacy Cortex cache client instrumentation doesn't track errors. #346
 * [CHANGE] Removed `CortexQuerierCapacityFull` alert. #342
 * [CHANGE] Changes blocks storage alerts to group metrics by the configured `cluster_labels` (supporting the deprecated `alert_aggregation_labels`). #351
+* [CHANGE] Increased `CortexIngesterReachingSeriesLimit` critical alert threshold from 80% to 85%. #363
 * [ENHANCEMENT] cortex-mixin: Make `cluster_namespace_deployment:kube_pod_container_resource_requests_{cpu_cores,memory_bytes}:sum` backwards compatible with `kube-state-metrics` v2.0.0. #317
 * [ENHANCEMENT] Cortex-mixin: Include `cortex-gw-internal` naming variation in default `gateway` job names. #328
 * [ENHANCEMENT] Ruler dashboard: added object storage metrics. #354
diff --git a/cortex-mixin/alerts/alerts.libsonnet b/cortex-mixin/alerts/alerts.libsonnet
index 9eefe7f8..be47dd7f 100644
--- a/cortex-mixin/alerts/alerts.libsonnet
+++ b/cortex-mixin/alerts/alerts.libsonnet
@@ -274,7 +274,7 @@
                 (cortex_ingester_memory_series / ignoring(limit) cortex_ingester_instance_limits{limit="max_series"})
                 and ignoring (limit)
                 (cortex_ingester_instance_limits{limit="max_series"} > 0)
-            ) > 0.8
+            ) > 0.85
           |||,
           'for': '5m',
           labels: {