diff --git a/internal/client/client_test.go b/internal/client/client_test.go
index 5a18fe6..1a0c1fa 100644
--- a/internal/client/client_test.go
+++ b/internal/client/client_test.go
@@ -255,10 +255,12 @@ func fakeIperf3(t *testing.T) string {
 	t.Helper()
 	path := filepath.Join(t.TempDir(), "iperf3")
 	script := `#!/bin/sh
-if echo "$@" | grep -q -- "-s"; then
-  sleep 10
-  exit 0
-fi
+for arg in "$@"; do
+  if [ "$arg" = "-s" ]; then
+    sleep 10
+    exit 0
+  fi
+done
 cat <<'JSON'
 {"end":{"sum_sent":{"bytes":1048576,"bits_per_second":88000000},"sum_received":{"bytes":1048576,"bits_per_second":87000000}}}
 JSON
diff --git a/internal/store/store.go b/internal/store/store.go
index 6ecd8e7..7ef2b73 100644
--- a/internal/store/store.go
+++ b/internal/store/store.go
@@ -20,6 +20,8 @@ type Store struct {
 	mu   sync.Mutex
 }
 
+const maxRecordLineBytes = 64 * 1024 * 1024
+
 type ClientInfo struct {
 	IP      string `json:"ip"`
 	ISP     string `json:"isp,omitempty"`
@@ -89,6 +91,7 @@ func (s *Store) List(ctx context.Context, limit int) ([]Record, error) {
 
 	var records []Record
 	scanner := bufio.NewScanner(file)
+	scanner.Buffer(make([]byte, 64*1024), maxRecordLineBytes)
 	for scanner.Scan() {
 		line := strings.TrimSpace(scanner.Text())
 		if line == "" {
diff --git a/internal/store/store_test.go b/internal/store/store_test.go
index e8ea92a..12de02c 100644
--- a/internal/store/store_test.go
+++ b/internal/store/store_test.go
@@ -121,3 +121,41 @@ func TestStoreListIgnoresBlankLinesAndMissingFile(t *testing.T) {
 		t.Fatalf("records order = %s, %s; want run-2, run-1", records[0].ID, records[1].ID)
 	}
 }
+
+func TestStoreListsLargeRecordsWithFullSampleCurves(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "records.jsonl")
+	store := New(path)
+	ctx := context.Background()
+
+	var samples []probe.Sample
+	for i := 0; i < 2000; i++ {
+		samples = append(samples, probe.Sample{
+			At:        time.Date(2026, 6, 10, 8, 0, 0, 0, time.UTC).Add(time.Duration(i) * time.Millisecond),
+			Kind:      "download",
+			Success:   true,
+			LatencyMS: 10.5,
+			Bytes:     4 * 1024 * 1024,
+			Mbps:      38.25,
+		})
+	}
+
+	if err := store.Append(ctx, Record{
+		ID:      "large-run",
+		Samples: samples,
+		Summary: probe.Summary{
+			ID:      "large-run",
+			Target:  "example.com:443",
+			Samples: len(samples),
+		},
+	}); err != nil {
+		t.Fatalf("Append large record: %v", err)
+	}
+
+	records, err := store.List(ctx, 10)
+	if err != nil {
+		t.Fatalf("List returned error: %v", err)
+	}
+	if len(records) != 1 || records[0].ID != "large-run" || len(records[0].Samples) != len(samples) {
+		t.Fatalf("records = %#v, want large record with %d samples", records, len(samples))
+	}
+}
diff --git a/internal/web/server_test.go b/internal/web/server_test.go
index 8603544..b397bff 100644
--- a/internal/web/server_test.go
+++ b/internal/web/server_test.go
@@ -1028,10 +1028,12 @@ func fakeIperf3(t *testing.T) string {
 	t.Helper()
 	path := filepath.Join(t.TempDir(), "iperf3")
 	script := `#!/bin/sh
-if echo "$@" | grep -q -- "-s"; then
-  sleep 10
-  exit 0
-fi
+for arg in "$@"; do
+  if [ "$arg" = "-s" ]; then
+    sleep 10
+    exit 0
+  fi
+done
 cat <<'JSON'
 {"end":{"sum_sent":{"bytes":1048576,"bits_per_second":88000000},"sum_received":{"bytes":1048576,"bits_per_second":87000000}}}
 JSON