diff --git a/cli/cmd/watch.go b/cli/cmd/watch.go
index 51acea3d..ef683645 100644
--- a/cli/cmd/watch.go
+++ b/cli/cmd/watch.go
@@ -75,6 +75,9 @@ type pollDoneMsg struct {
 const maxStaleRetries = 5
 const maxConnRetries = 10
 
+// sparklinePoints is how many polls the throughput sparkline shows.
+const sparklinePoints = 40
+
 type pollModel struct {
 	ctx            context.Context
 	id             string
@@ -188,6 +191,11 @@ func (m pollModel) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 		}
 		m.recordsSent = totalSent
 		m.throughputHist = append(m.throughputHist, maxThroughput)
+		// The whole run's history grew without bound: an hour in, the
+		// sparkline was 1,823 columns and the live number was cut off.
+		if len(m.throughputHist) > sparklinePoints {
+			m.throughputHist = m.throughputHist[len(m.throughputHist)-sparklinePoints:]
+		}
 
 		if test.Spec != nil && test.Spec.Records > 0 {
 			m.totalRecords = float64(test.Spec.Records)
diff --git a/cli/cmd/watch_test.go b/cli/cmd/watch_test.go
index 8a9ee4ca..147a3d01 100644
--- a/cli/cmd/watch_test.go
+++ b/cli/cmd/watch_test.go
@@ -9,6 +9,7 @@ import (
 	"time"
 
 	"github.com/bmscomp/kates/cli/client"
+	tea "github.com/charmbracelet/bubbletea"
 )
 
 // stubPoll scripts a sequence of GetTest responses and restores the seams on
@@ -41,6 +42,21 @@ func run(status string, sent float64) func() (*client.TestRun, error) {
 	}
 }
 
+// The throughput sparkline kept every poll of the run: an hour in it was 1,823
+// columns wide, and the renderer cut off the live number after it.
+func TestPollModel_SparklineKeepsTheLastPoints(t *testing.T) {
+	var m tea.Model = pollModel{id: "test-1234"}
+	for i := range 100 {
+		m, _ = m.Update(pollResultMsg{test: &client.TestRun{ID: "test-1234", Status: "RUNNING",
+			Results: []client.PhaseResult{{ThroughputRecordsPerSec: float64(i)}}}})
+	}
+	hist := m.(pollModel).throughputHist
+	if len(hist) != sparklinePoints || hist[0] != 100-sparklinePoints || hist[len(hist)-1] != 99 {
+		t.Errorf("history = %d points from %v to %v, want the last %d, 60 to 99",
+			len(hist), hist[0], hist[len(hist)-1], sparklinePoints)
+	}
+}
+
 // The flagship contract: a FAILED test is reported as FAILED, never swallowed.
 // The previous pollUntilDone returned nothing at all — the TUI printed "Test
 // failed" and callers exited 0, keeping CI green on failed load tests.