diff --git a/Library/Homebrew/tap.rb b/Library/Homebrew/tap.rb
index 1b487f52fa..bf83e7ee29 100644
--- a/Library/Homebrew/tap.rb
+++ b/Library/Homebrew/tap.rb
@@ -590,8 +590,9 @@ class Tap
     end
     return unless remote
 
-    current_upstream_head = T.must(git_repository.origin_branch_name)
-    return if requested_remote.blank? && git_repository.origin_has_branch?(current_upstream_head)
+    current_upstream_head = git_repository.origin_branch_name
+    return if current_upstream_head.present? && requested_remote.blank? &&
+              git_repository.origin_has_branch?(current_upstream_head)
 
     args = %w[fetch]
     args << "--quiet" if quiet
@@ -600,6 +601,8 @@ class Tap
     safe_system "git", "-C", path, *args
     git_repository.set_head_origin_auto
 
+    current_upstream_head ||= T.must(git_repository.origin_branch_name)
+
     new_upstream_head = T.must(git_repository.origin_branch_name)
     return if new_upstream_head == current_upstream_head