diff --git a/docs/configuration/config-file-reference.md b/docs/configuration/config-file-reference.md
index ce52ee95ae..5db4fe4b7e 100644
--- a/docs/configuration/config-file-reference.md
+++ b/docs/configuration/config-file-reference.md
@@ -3591,7 +3591,7 @@ query_rejection:
 
 # Index size limit in bytes for each compaction partition. 0 means no limit
 # CLI flag: -compactor.partition-index-size-limit-in-bytes
-[compactor_partition_index_size_limit_in_bytes: <int> | default = 0]
+[compactor_partition_index_size_limit_in_bytes: <int> | default = 68719476736]
 
 # Time series count limit for each compaction partition. 0 means no limit
 # CLI flag: -compactor.partition-series-count-limit
diff --git a/pkg/util/validation/limits.go b/pkg/util/validation/limits.go
index 32a24f18bc..11458c8165 100644
--- a/pkg/util/validation/limits.go
+++ b/pkg/util/validation/limits.go
@@ -284,7 +284,8 @@ func (l *Limits) RegisterFlags(f *flag.FlagSet) {
 
 	f.Var(&l.CompactorBlocksRetentionPeriod, "compactor.blocks-retention-period", "Delete blocks containing samples older than the specified retention period. 0 to disable.")
 	f.IntVar(&l.CompactorTenantShardSize, "compactor.tenant-shard-size", 0, "The default tenant's shard size when the shuffle-sharding strategy is used by the compactor. When this setting is specified in the per-tenant overrides, a value of 0 disables shuffle sharding for the tenant.")
-	f.Int64Var(&l.CompactorPartitionIndexSizeLimitInBytes, "compactor.partition-index-size-limit-in-bytes", 0, "Index size limit in bytes for each compaction partition. 0 means no limit")
+	// Default to 64GB because this is the hard limit of index size in Cortex
+	f.Int64Var(&l.CompactorPartitionIndexSizeLimitInBytes, "compactor.partition-index-size-limit-in-bytes", 68719476736, "Index size limit in bytes for each compaction partition. 0 means no limit")
 	f.Int64Var(&l.CompactorPartitionSeriesCountLimit, "compactor.partition-series-count-limit", 0, "Time series count limit for each compaction partition. 0 means no limit")
 
 	// Store-gateway.