diff --git a/.changeset/metrics-batch-str-data-index.md b/.changeset/metrics-batch-str-data-index.md
new file mode 100644
index 000000000..e0cc37e8a
--- /dev/null
+++ b/.changeset/metrics-batch-str-data-index.md
@@ -0,0 +1,5 @@
+---
+"github.com/livekit/protocol": patch
+---
+
+`utils.MetricsBatchBuilder.Merge` rejects out-of-range `str_data` indexes on 32-bit builds.
diff --git a/utils/metrics_batch_builder.go b/utils/metrics_batch_builder.go
index d6fc54e21..1a12ae6f3 100644
--- a/utils/metrics_batch_builder.go
+++ b/utils/metrics_batch_builder.go
@@ -309,7 +309,7 @@ func (m *MetricsBatchBuilder) translateStrDataIndex(strData []string, index uint
 	}
 
 	baseIdx := index - uint32(livekit.MetricLabel_METRIC_LABEL_PREDEFINED_MAX_VALUE)
-	if len(strData) <= int(baseIdx) {
+	if uint64(len(strData)) <= uint64(baseIdx) {
 		return 0, false
 	}
 
@@ -325,7 +325,7 @@ func getStrDataForIndex(mb *livekit.MetricsBatch, index uint32) (string, bool) {
 	}
 
 	baseIdx := index - uint32(livekit.MetricLabel_METRIC_LABEL_PREDEFINED_MAX_VALUE)
-	if len(mb.StrData) <= int(baseIdx) {
+	if uint64(len(mb.StrData)) <= uint64(baseIdx) {
 		return "", false
 	}
 
diff --git a/utils/metrics_batch_builder_test.go b/utils/metrics_batch_builder_test.go
index a5774be93..fbc9d93df 100644
--- a/utils/metrics_batch_builder_test.go
+++ b/utils/metrics_batch_builder_test.go
@@ -596,4 +596,31 @@ func TestMetricsBatchBuilder(t *testing.T) {
 		mb := mbb.ToProto()
 		require.True(t, proto.Equal(expected, mb))
 	})
+
+	t.Run("merge str data index beyond int32", func(t *testing.T) {
+		// index past the end must be rejected even where int is 32 bits
+		const huge = ^uint32(0)
+		mbb := NewMetricsBatchBuilder()
+		require.NotPanics(t, func() {
+			mbb.Merge(&livekit.MetricsBatch{
+				StrData: []string{"PA"},
+				TimeSeries: []*livekit.TimeSeriesMetric{
+					{Label: huge, ParticipantIdentity: huge, TrackSid: huge, Rid: huge},
+					{Label: uint32(livekit.MetricLabel_SUBSCRIBER_RTT), ParticipantIdentity: huge},
+				},
+				Events: []*livekit.EventMetric{
+					{Label: huge, ParticipantIdentity: huge, TrackSid: huge, Rid: huge},
+					{Label: uint32(livekit.MetricLabel_SUBSCRIBER_RTT), ParticipantIdentity: huge},
+				},
+			})
+		})
+		mb := mbb.ToProto()
+		require.Len(t, mb.TimeSeries, 2)
+		require.Len(t, mb.Events, 2)
+		require.Empty(t, mb.StrData)
+		for _, ts := range mb.TimeSeries {
+			require.Zero(t, ts.ParticipantIdentity)
+			require.Zero(t, ts.TrackSid)
+		}
+	})
 }