diff --git a/notifications/endpoint.go b/notifications/endpoint.go
index 29a9e27b..44d0f6d7 100644
--- a/notifications/endpoint.go
+++ b/notifications/endpoint.go
@@ -13,7 +13,7 @@ type EndpointConfig struct {
 	Threshold         int
 	Backoff           time.Duration
 	IgnoredMediaTypes []string
-	Transport         *http.Transport
+	Transport         *http.Transport `json:"-"`
 }
 
 // defaults set any zero-valued fields to a reasonable default.
diff --git a/notifications/metrics_test.go b/notifications/metrics_test.go
new file mode 100644
index 00000000..03a08e2c
--- /dev/null
+++ b/notifications/metrics_test.go
@@ -0,0 +1,28 @@
+package notifications
+
+import (
+	"encoding/json"
+	"expvar"
+	"testing"
+)
+
+func TestMetricsExpvar(t *testing.T) {
+	endpointsVar := expvar.Get("registry").(*expvar.Map).Get("notifications").(*expvar.Map).Get("endpoints")
+
+	var v interface{}
+	if err := json.Unmarshal([]byte(endpointsVar.String()), &v); err != nil {
+		t.Fatalf("unexpected error unmarshaling endpoints: %v", err)
+	}
+	if v != nil {
+		t.Fatalf("expected nil, got %#v", v)
+	}
+
+	NewEndpoint("x", "y", EndpointConfig{})
+
+	if err := json.Unmarshal([]byte(endpointsVar.String()), &v); err != nil {
+		t.Fatalf("unexpected error unmarshaling endpoints: %v", err)
+	}
+	if slice, ok := v.([]interface{}); !ok || len(slice) != 1 {
+		t.Logf("expected one-element []interface{}, got %#v", v)
+	}
+}
diff --git a/registry/storage/tagstore.go b/registry/storage/tagstore.go
index 4386ffca..be7baf87 100644
--- a/registry/storage/tagstore.go
+++ b/registry/storage/tagstore.go
@@ -122,17 +122,20 @@ func (ts *tagStore) Untag(ctx context.Context, tag string) error {
 		name: ts.repository.Named().Name(),
 		tag:  tag,
 	})
-
-	switch err.(type) {
-	case storagedriver.PathNotFoundError:
-		return distribution.ErrTagUnknown{Tag: tag}
-	case nil:
-		break
-	default:
+	if err != nil {
 		return err
 	}
 
-	return ts.blobStore.driver.Delete(ctx, tagPath)
+	if err := ts.blobStore.driver.Delete(ctx, tagPath); err != nil {
+		switch err.(type) {
+		case storagedriver.PathNotFoundError:
+			return nil // Untag is idempotent, we don't care if it didn't exist
+		default:
+			return err
+		}
+	}
+
+	return nil
 }
 
 // linkedBlobStore returns the linkedBlobStore for the named tag, allowing one
@@ -179,6 +182,10 @@ func (ts *tagStore) Lookup(ctx context.Context, desc distribution.Descriptor) ([
 		tagLinkPath, err := pathFor(tagLinkPathSpec)
 		tagDigest, err := ts.blobStore.readlink(ctx, tagLinkPath)
 		if err != nil {
+			switch err.(type) {
+			case storagedriver.PathNotFoundError:
+				continue
+			}
 			return nil, err
 		}
 
diff --git a/registry/storage/tagstore_test.go b/registry/storage/tagstore_test.go
index 554a46bf..0c8e3611 100644
--- a/registry/storage/tagstore_test.go
+++ b/registry/storage/tagstore_test.go
@@ -84,8 +84,8 @@ func TestTagStoreUnTag(t *testing.T) {
 	desc := distribution.Descriptor{Digest: "sha256:bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb"}
 
 	err := tags.Untag(ctx, "latest")
-	if err == nil {
-		t.Errorf("Expected error untagging non-existant tag")
+	if err != nil {
+		t.Error(err)
 	}
 
 	err = tags.Tag(ctx, "latest", desc)