diff --git a/cmd/buildpack/main.go b/cmd/buildpack/main.go
index 5d8790b..090dfa8 100644
--- a/cmd/buildpack/main.go
+++ b/cmd/buildpack/main.go
@@ -126,7 +126,7 @@ func (s *server) serveBuildpackManifest(w http.ResponseWriter, r *http.Request)
 	// image tag.
 	if commitRE.MatchString(revision) {
 		ck := cacheKey(path, revision)
-		if err := s.storage.BlobExists(ctx, ck); err == nil {
+		if _, err := s.storage.BlobExists(ctx, ck); err == nil {
 			s.info.Println("serving cached manifest:", ck)
 			serve.Blob(w, r, ck)
 			return
@@ -231,7 +231,7 @@ func (s *server) prepareWorkspace() (string, string, error) {
 }
 
 func (s *server) fetchAndBuild(src, layers, ghOwner, ghRepo, revision, path string) (string, error) {
-	image := fmt.Sprintf("gcr.io/%s/built-%d", projectID, time.Now().Unix)
+	image := fmt.Sprintf("gcr.io/%s/built-%d", projectID, time.Now().Unix())
 	source := fmt.Sprintf("https://github.com/%s/%s/archive/%s.tar.gz", ghOwner, ghRepo, revision)
 
 	if resp, err := http.Head(source); err != nil {
diff --git a/cmd/flatten/main.go b/cmd/flatten/main.go
index 7f78ae1..a87705a 100644
--- a/cmd/flatten/main.go
+++ b/cmd/flatten/main.go
@@ -108,7 +108,7 @@ func (s *server) serveFlattenManifest(w http.ResponseWriter, r *http.Request) {
 	// Check if we have a flattened manifest cached, and if so serve it
 	// directly.
 	ck := cacheKey(d.Digest.String())
-	if err := s.storage.BlobExists(ctx, ck); err == nil {
+	if _, err := s.storage.BlobExists(ctx, ck); err == nil {
 		s.info.Println("serving cached manifest:", ck)
 		serve.Blob(w, r, ck)
 		return
diff --git a/cmd/kaniko/main.go b/cmd/kaniko/main.go
index 98cb4dc..97e86ad 100644
--- a/cmd/kaniko/main.go
+++ b/cmd/kaniko/main.go
@@ -119,7 +119,7 @@ func (s *server) serveKanikoManifest(w http.ResponseWriter, r *http.Request) {
 	// image tag.
 	if commitRE.MatchString(revision) {
 		ck := cacheKey(path, revision)
-		if err := s.storage.BlobExists(ctx, ck); err == nil {
+		if _, err := s.storage.BlobExists(ctx, ck); err == nil {
 			s.info.Println("serving cached manifest:", ck)
 			serve.Blob(w, r, ck)
 			return
@@ -223,7 +223,7 @@ func (s *server) prepareWorkspace() error {
 }
 
 func (s *server) fetchAndBuild(ghOwner, ghRepo, revision, path string) (string, error) {
-	image := fmt.Sprintf("gcr.io/%s/built-%d", projectID, time.Now().Unix)
+	image := fmt.Sprintf("gcr.io/%s/built-%d", projectID, time.Now().Unix())
 	source := fmt.Sprintf("https://github.com/%s/%s/archive/%s.tar.gz", ghOwner, ghRepo, revision)
 
 	if resp, err := http.Head(source); err != nil {
diff --git a/cmd/mirror/main.go b/cmd/mirror/main.go
index 6b0065f..c92dddb 100644
--- a/cmd/mirror/main.go
+++ b/cmd/mirror/main.go
@@ -89,6 +89,21 @@ func (s *server) serveMirrorManifest(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// If it's a HEAD request, and request was by digest, and we have that
+	// manifest mirrored by digest already, serve HEAD response from GCS.
+	// If it's a HEAD request and the other conditions aren't met, we'll
+	// handle this later by consulting the real registry.
+	if r.Method == http.MethodHead {
+		if d, ok := ref.(name.Digest); ok {
+			if desc, err := s.storage.BlobExists(ctx, d.DigestStr()); err == nil {
+				w.Header().Set("Docker-Content-Digest", d.DigestStr())
+				w.Header().Set("Content-Type", string(desc.MediaType))
+				w.Header().Set("Content-Length", fmt.Sprintf("%d", desc.Size))
+				return
+			}
+		}
+	}
+
 	// Get the original image's digest, and check if we have that manifest
 	// blob.
 	d, err := remote.Head(ref, remote.WithContext(ctx))
@@ -97,7 +112,13 @@ func (s *server) serveMirrorManifest(w http.ResponseWriter, r *http.Request) {
 		serve.Error(w, err)
 		return
 	}
-	if err := s.storage.BlobExists(ctx, d.Digest.String()); err == nil {
+	if r.Method == http.MethodHead {
+		w.Header().Set("Docker-Content-Digest", d.Digest.String())
+		w.Header().Set("Content-Type", string(d.MediaType))
+		w.Header().Set("Content-Length", fmt.Sprintf("%d", d.Size))
+		return
+	}
+	if _, err := s.storage.BlobExists(ctx, d.Digest.String()); err == nil {
 		serve.Blob(w, r, d.Digest.String())
 		return
 	} else {
diff --git a/cmd/wait/main.go b/cmd/wait/main.go
index 0b29af3..865e3cf 100644
--- a/cmd/wait/main.go
+++ b/cmd/wait/main.go
@@ -86,7 +86,7 @@ func (s *server) serveWaitManifest(w http.ResponseWriter, r *http.Request) {
 
 	// The image has already been built; serve it.
 	ck := cacheKey(name)
-	if err := s.storage.BlobExists(ctx, ck); err == nil {
+	if _, err := s.storage.BlobExists(ctx, ck); err == nil {
 		s.info.Printf("blob %q exists, serving", ck)
 		serve.Blob(w, r, ck)
 		return
@@ -95,7 +95,7 @@ func (s *server) serveWaitManifest(w http.ResponseWriter, r *http.Request) {
 	// If a placeholder exists, a wait is ongoing; serve the placeholder
 	// contents.
 	phn := fmt.Sprintf("placeholder-%s", ck)
-	if err := s.storage.BlobExists(ctx, phn); err == nil {
+	if _, err := s.storage.BlobExists(ctx, phn); err == nil {
 		s.info.Printf("placeholder %q exists", phn)
 		serve.Error(w, fmt.Errorf("waiting for image..."))
 		return
@@ -143,7 +143,7 @@ const size = 100
 const num = 10
 
 var laterFunc = delay.Func("later", func(ctx context.Context, ck string) error {
-	log.Println("generating random image for cache key %q", ck)
+	log.Printf("generating random image for cache key %q", ck)
 	img, err := random.Image(size, num)
 	if err != nil {
 		return err
diff --git a/pkg/serve/serve.go b/pkg/serve/serve.go
index 99e0de4..315f6e3 100644
--- a/pkg/serve/serve.go
+++ b/pkg/serve/serve.go
@@ -13,6 +13,7 @@ import (
 
 	"cloud.google.com/go/storage"
 	v1 "github.com/google/go-containerregistry/pkg/v1"
+	"github.com/google/go-containerregistry/pkg/v1/types"
 	"golang.org/x/sync/errgroup"
 	"google.golang.org/api/googleapi"
 )
@@ -36,9 +37,15 @@ func NewStorage(ctx context.Context) (*Storage, error) {
 	return &Storage{client}, nil
 }
 
-func (s *Storage) BlobExists(ctx context.Context, name string) error {
-	_, err := s.client.Bucket(bucket).Object(fmt.Sprintf("blobs/%s", name)).Attrs(ctx)
-	return err
+func (s *Storage) BlobExists(ctx context.Context, name string) (v1.Descriptor, error) {
+	obj, err := s.client.Bucket(bucket).Object(fmt.Sprintf("blobs/%s", name)).Attrs(ctx)
+	if err != nil {
+		return v1.Descriptor{}, err
+	}
+	return v1.Descriptor{
+		MediaType: types.MediaType(obj.ContentType),
+		Size:      obj.Size,
+	}, nil
 }
 
 func (s *Storage) WriteObject(ctx context.Context, name, contents string) error {