diff --git a/Formula/git-when-merged.rb b/Formula/git-when-merged.rb
index 8efb7e19452b..6209fe4d2644 100644
--- a/Formula/git-when-merged.rb
+++ b/Formula/git-when-merged.rb
@@ -26,6 +26,7 @@ def install
   end
 
   test do
+    system "git", "config", "--global", "init.defaultBranch", "master"
     system "git", "init"
     system "git", "config", "user.name", "BrewTestBot"
     system "git", "config", "user.email", "BrewTestBot@example.com"