diff --git a/aperture.go b/aperture.go
index 35cec7d..c417112 100644
--- a/aperture.go
+++ b/aperture.go
@@ -151,7 +151,7 @@ func run() error {
 
 	errChan := make(chan error)
 	a := NewAperture(cfg)
-	if err := a.Start(errChan); err != nil {
+	if err := a.Start(errChan, interceptor.ShutdownChannel()); err != nil {
 		return fmt.Errorf("unable to start aperture: %v", err)
 	}
 
@@ -192,9 +192,9 @@ func NewAperture(cfg *Config) *Aperture {
 }
 
 // Start sets up the proxy server and starts it.
-func (a *Aperture) Start(errChan chan error) error {
+func (a *Aperture) Start(errChan chan error, shutdown <-chan struct{}) error {
 	// Start the prometheus exporter.
-	err := StartPrometheusExporter(a.cfg.Prometheus)
+	err := StartPrometheusExporter(a.cfg.Prometheus, shutdown)
 	if err != nil {
 		return fmt.Errorf("unable to start the prometheus "+
 			"exporter: %v", err)
diff --git a/hashmail_server.go b/hashmail_server.go
index 69822d3..0c03276 100644
--- a/hashmail_server.go
+++ b/hashmail_server.go
@@ -809,9 +809,9 @@ func (sa *streamActivity) Record(baseID string) {
 // ClassifyAndReset categorizes each tracked stream based on its recent read
 // rate and returns aggregate counts of active, standby, and in-use sessions.
 // A stream is classified as:
-// - In-use:   if read rate ≥ 0.5 reads/sec
-// - Standby:  if 0 < read rate < 0.5 reads/sec
-// - Active:   if read rate > 0 (includes standby and in-use)
+// - In-use:   if read rate ≥ 0.5 reads/sec.
+// - Standby:  if 0 < read rate < 0.5 reads/sec.
+// - Active:   if read rate > 0 (includes standby and in-use).
 func (sa *streamActivity) ClassifyAndReset() (active, standby, inuse int) {
 	sa.Lock()
 	defer sa.Unlock()
diff --git a/hashmail_server_test.go b/hashmail_server_test.go
index 609dff9..d4a4848 100644
--- a/hashmail_server_test.go
+++ b/hashmail_server_test.go
@@ -186,7 +186,8 @@ func setupAperture(t *testing.T) {
 	}
 	aperture := NewAperture(apertureCfg)
 	errChan := make(chan error)
-	require.NoError(t, aperture.Start(errChan))
+	shutdown := make(chan struct{})
+	require.NoError(t, aperture.Start(errChan, shutdown))
 
 	// Any error while starting?
 	select {
diff --git a/prometheus.go b/prometheus.go
index 353d63e..c921667 100644
--- a/prometheus.go
+++ b/prometheus.go
@@ -16,21 +16,21 @@ var (
 		Name:      "mailbox_count",
 	})
 
-	// activeSessions tracks the active session count for mailbox
+	// activeSessions tracks the active session count for mailbox.
 	activeSessions = prometheus.NewGauge(prometheus.GaugeOpts{
 		Namespace: "hashmail",
 		Name:      "mailbox_active_sessions",
 		Help:      "Number of active sessions",
 	})
 
-	// standbySessions tracks the standby session count for mailbox
+	// standbySessions tracks the standby session count for mailbox.
 	standbySessions = prometheus.NewGauge(prometheus.GaugeOpts{
 		Namespace: "hashmail",
 		Name:      "mailbox_standby_sessions",
 		Help:      "Number of standby sessions",
 	})
 
-	// inUseSessions tracks the in-use session count for mailbox
+	// inUseSessions tracks the in-use session count for mailbox.
 	inUseSessions = prometheus.NewGauge(prometheus.GaugeOpts{
 		Namespace: "hashmail",
 		Name:      "mailbox_inuse_sessions",
@@ -38,7 +38,7 @@ var (
 	})
 )
 
-// streamActivityTracker handles the calculation of session statistics
+// streamActivityTracker handles the calculation of session statistics.
 var streamActivityTracker = newStreamActivity()
 
 // PrometheusConfig is the set of configuration data that specifies if
@@ -56,7 +56,9 @@ type PrometheusConfig struct {
 // StartPrometheusExporter registers all relevant metrics with the Prometheus
 // library, then launches the HTTP server that Prometheus will hit to scrape
 // our metrics.
-func StartPrometheusExporter(cfg *PrometheusConfig) error {
+func StartPrometheusExporter(cfg *PrometheusConfig,
+	shutdown <-chan struct{}) error {
+
 	// If we're not active, then there's nothing more to do.
 	if !cfg.Enabled {
 		return nil
@@ -68,16 +70,23 @@ func StartPrometheusExporter(cfg *PrometheusConfig) error {
 	prometheus.MustRegister(standbySessions)
 	prometheus.MustRegister(inUseSessions)
 
-	// Periodically update session classification metrics from internal tracker
+	// Periodically update session classification metrics from internal tracker.
 	go func() {
 		ticker := time.NewTicker(10 * time.Second)
 		defer ticker.Stop()
 
-		for range ticker.C {
-			active, standby, inuse := streamActivityTracker.ClassifyAndReset()
-			activeSessions.Set(float64(active))
-			standbySessions.Set(float64(standby))
-			inUseSessions.Set(float64(inuse))
+		for {
+			select {
+			case <-ticker.C:
+				active, standby, inuse :=
+					streamActivityTracker.ClassifyAndReset()
+				activeSessions.Set(float64(active))
+				standbySessions.Set(float64(standby))
+				inUseSessions.Set(float64(inuse))
+			case <-shutdown:
+				log.Infof("Shutting down Prometheus session metrics updater")
+				return
+			}
 		}
 	}()