diff --git a/buildfile.go b/buildfile.go
index 2b6d40c15d..19249b04c4 100644
--- a/buildfile.go
+++ b/buildfile.go
@@ -630,7 +630,13 @@ func (b *buildFile) Build(context io.Reader) (string, error) {
 	if err != nil {
 		return "", err
 	}
-	b.context = &utils.TarSum{Reader: context, DisableCompression: true}
+
+	decompressedStream, err := archive.DecompressStream(context)
+	if err != nil {
+		return "", err
+	}
+
+	b.context = &utils.TarSum{Reader: decompressedStream, DisableCompression: true}
 	if err := archive.Untar(b.context, tmpdirPath, nil); err != nil {
 		return "", err
 	}