diff --git a/remotes/docker/resolver.go b/remotes/docker/resolver.go
index 5258d7179..2188ae383 100644
--- a/remotes/docker/resolver.go
+++ b/remotes/docker/resolver.go
@@ -521,7 +521,10 @@ func (r *request) do(ctx context.Context) (*http.Response, error) {
 	if err != nil {
 		return nil, err
 	}
-	req.Header = r.header
+	req.Header = http.Header{} // headers need to be copied to avoid concurrent map access
+	for k, v := range r.header {
+		req.Header[k] = v
+	}
 	if r.body != nil {
 		body, err := r.body()
 		if err != nil {