diff --git a/cmd/prometheus/main.go b/cmd/prometheus/main.go
index 4559d51837..ef76084217 100644
--- a/cmd/prometheus/main.go
+++ b/cmd/prometheus/main.go
@@ -455,7 +455,7 @@ func main() {
 
 	agentOnlyFlag(a, "storage.agent.wal-truncate-frequency",
 		"The frequency at which to truncate the WAL and remove old data.").
-		Hidden().PlaceHolder("<duration>").SetValue(&cfg.agent.TruncateFrequency)
+		Default("2h").PlaceHolder("<duration>").SetValue(&cfg.agent.TruncateFrequency)
 
 	agentOnlyFlag(a, "storage.agent.retention.min-time",
 		"Minimum age samples may be before being considered for deletion when the WAL is truncated").
diff --git a/docs/command-line/prometheus.md b/docs/command-line/prometheus.md
index 9b4ec8b736..4c2eabe583 100644
--- a/docs/command-line/prometheus.md
+++ b/docs/command-line/prometheus.md
@@ -43,6 +43,7 @@ The Prometheus monitoring server
 | <code class="text-nowrap">--storage.tsdb.head-chunks-write-queue-size</code> | Size of the queue through which head chunks are written to the disk to be m-mapped, 0 disables the queue completely. Experimental. Use with server mode only. | `0` |
 | <code class="text-nowrap">--storage.agent.path</code> | Base path for metrics storage. Use with agent mode only. | `data-agent/` |
 | <code class="text-nowrap">--storage.agent.wal-compression</code> | Compress the agent WAL. Use with agent mode only. | `true` |
+| <code class="text-nowrap">--storage.agent.wal-truncate-frequency</code> | The frequency at which to truncate the WAL and remove old data. Use with agent mode only. | `2h` |
 | <code class="text-nowrap">--storage.agent.retention.min-time</code> | Minimum age samples may be before being considered for deletion when the WAL is truncated Use with agent mode only. |  |
 | <code class="text-nowrap">--storage.agent.retention.max-time</code> | Maximum age samples may be before being forcibly deleted when the WAL is truncated Use with agent mode only. |  |
 | <code class="text-nowrap">--storage.agent.no-lockfile</code> | Do not create lockfile in data directory. Use with agent mode only. | `false` |