diff --git a/api/pkg/artifact/artifact.go b/api/pkg/artifact/artifact.go
index 5b5df578..af7857bc 100644
--- a/api/pkg/artifact/artifact.go
+++ b/api/pkg/artifact/artifact.go
@@ -27,7 +27,7 @@ type Service interface {
 	ParseURL(gsURL string) (*URL, error)
 
 	ReadArtifact(ctx context.Context, url string) ([]byte, error)
-	WriteArtifact(ctx context.Context, url, content string) error
+	WriteArtifact(ctx context.Context, url string, content []byte) error
 	DeleteArtifact(ctx context.Context, url string) error
 }
 
@@ -88,14 +88,14 @@ func (gac *GcsArtifactClient) ReadArtifact(ctx context.Context, url string) ([]b
 	return bytes, nil
 }
 
-func (gac *GcsArtifactClient) WriteArtifact(ctx context.Context, url, content string) error {
+func (gac *GcsArtifactClient) WriteArtifact(ctx context.Context, url string, content []byte) error {
 	u, err := gac.ParseURL(url)
 	if err != nil {
 		return err
 	}
 	w := gac.API.Bucket(u.Bucket).Object(u.Object).NewWriter(ctx)
 
-	if _, err := fmt.Fprint(w, content); err != nil {
+	if _, err := fmt.Fprintf(w, "%s", content); err != nil {
 		return err
 	}
 
@@ -147,7 +147,7 @@ func (nac *NopArtifactClient) ReadArtifact(ctx context.Context, url string) ([]b
 	return nil, nil
 }
 
-func (nac *NopArtifactClient) WriteArtifact(ctx context.Context, url, content string) error {
+func (nac *NopArtifactClient) WriteArtifact(ctx context.Context, url string, content []byte) error {
 	return nil
 }
 
diff --git a/api/pkg/artifact/mocks/artifact.go b/api/pkg/artifact/mocks/artifact.go
index 426e9bea..36e785c7 100644
--- a/api/pkg/artifact/mocks/artifact.go
+++ b/api/pkg/artifact/mocks/artifact.go
@@ -82,11 +82,11 @@ func (_m *Service) ReadArtifact(ctx context.Context, url string) ([]byte, error)
 }
 
 // WriteArtifact provides a mock function with given fields: ctx, url, content
-func (_m *Service) WriteArtifact(ctx context.Context, url string, content string) error {
+func (_m *Service) WriteArtifact(ctx context.Context, url string, content []byte) error {
 	ret := _m.Called(ctx, url, content)
 
 	var r0 error
-	if rf, ok := ret.Get(0).(func(context.Context, string, string) error); ok {
+	if rf, ok := ret.Get(0).(func(context.Context, string, []byte) error); ok {
 		r0 = rf(ctx, url, content)
 	} else {
 		r0 = ret.Error(0)