diff --git a/build/url.go b/build/url.go
index 60cf28e6..9188b1b0 100644
--- a/build/url.go
+++ b/build/url.go
@@ -7,13 +7,15 @@ import (
 
 	"github.com/docker/buildx/driver"
 	"github.com/docker/buildx/util/progress"
+	"github.com/docker/go-units"
 	"github.com/moby/buildkit/client"
 	"github.com/moby/buildkit/client/llb"
 	gwclient "github.com/moby/buildkit/frontend/gateway/client"
 	"github.com/pkg/errors"
-	"google.golang.org/protobuf/proto"
 )
 
+const maxDockerfileSize = 2 * 1024 * 1024 // 2 MB
+
 func createTempDockerfileFromURL(ctx context.Context, d *driver.DriverHandle, url string, pw progress.Writer) (string, error) {
 	c, err := driver.Boot(ctx, ctx, d, pw)
 	if err != nil {
@@ -44,8 +46,8 @@ func createTempDockerfileFromURL(ctx context.Context, d *driver.DriverHandle, ur
 		if err != nil {
 			return nil, err
 		}
-		if proto.Size(stat) > 512*1024 {
-			return nil, errors.Errorf("Dockerfile %s bigger than allowed max size", url)
+		if stat.Size > maxDockerfileSize {
+			return nil, errors.Errorf("Dockerfile %s bigger than allowed max size (%s)", url, units.HumanSize(maxDockerfileSize))
 		}
 
 		dt, err := ref.ReadFile(ctx, gwclient.ReadRequest{