diff --git a/remotes/docker/authorizer.go b/remotes/docker/authorizer.go
index e17628750..73adb5a2f 100644
--- a/remotes/docker/authorizer.go
+++ b/remotes/docker/authorizer.go
@@ -194,7 +194,11 @@ func (a *dockerAuthorizer) fetchTokenWithOAuth(ctx context.Context, to tokenOpti
 		form.Set("password", to.secret)
 	}
 
-	resp, err := ctxhttp.PostForm(ctx, a.client, to.realm, form)
+	resp, err := ctxhttp.Post(
+		ctx, a.client, to.realm,
+		"application/x-www-form-urlencoded; charset=utf-8",
+		strings.NewReader(form.Encode()),
+	)
 	if err != nil {
 		return "", err
 	}