diff --git a/prometheus/histogram.go b/prometheus/histogram.go
index 63a3d3b..36cf415 100644
--- a/prometheus/histogram.go
+++ b/prometheus/histogram.go
@@ -480,7 +480,7 @@ func makeSparseBuckets(buckets *sync.Map) *dto.SparseBuckets {
 		count := atomic.LoadUint64(v.(*uint64))
 		if n == 0 || i-nextI != 0 {
 			sbs.Span = append(sbs.Span, &dto.SparseBuckets_Span{
-				Offset: proto.Int(i - nextI),
+				Offset: proto.Int32(int32(i - nextI)),
 				Length: proto.Uint32(1),
 			})
 		} else {