diff --git a/CHANGELOG.md b/CHANGELOG.md
index 72f8f180..e26b1548 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -14,6 +14,7 @@ We use *breaking :warning:* to mark changes that are not backward compatible (re
 - [#33](https://github.com/thanos-io/objstore/pull/33) Tracing: Add `ContextWithTracer()` to inject the tracer into the context.
 - [#34](https://github.com/thanos-io/objstore/pull/34) Fix ignored options when creating shared credential Azure client.
 - [#62](https://github.com/thanos-io/objstore/pull/62) S3: Fix ignored context cancellation in `Iter` method.
+- [#77](https://github.com/thanos-io/objstore/pull/77) Fix buckets wrapped with metrics from being unable to determine object sizes in `Upload`.
 
 ### Added
 - [#15](https://github.com/thanos-io/objstore/pull/15) Add Oracle Cloud Infrastructure Object Storage Bucket support.
diff --git a/objstore.go b/objstore.go
index 5bcc55f1..20723704 100644
--- a/objstore.go
+++ b/objstore.go
@@ -594,7 +594,7 @@ func (b *metricBucket) Upload(ctx context.Context, name string, r io.Reader) err
 	b.ops.WithLabelValues(op).Inc()
 
 	trc := newTimingReadCloser(
-		io.NopCloser(r),
+		NopCloserWithSize(r),
 		op,
 		b.opsDuration,
 		b.opsFailures,