diff --git a/Formula/asn1c.rb b/Formula/asn1c.rb
index 9d735347614..3d2404baa6e 100644
--- a/Formula/asn1c.rb
+++ b/Formula/asn1c.rb
@@ -18,7 +18,7 @@ class Asn1c < Formula
   end
 
   head do
-    url "https://github.com/vlm/asn1c.git"
+    url "https://github.com/vlm/asn1c.git", branch: "master"
     depends_on "autoconf" => :build
     depends_on "automake" => :build
     depends_on "libtool" => :build