diff --git a/Library/Homebrew/download_queue.rb b/Library/Homebrew/download_queue.rb
index 076135389c..c0987742c7 100644
--- a/Library/Homebrew/download_queue.rb
+++ b/Library/Homebrew/download_queue.rb
@@ -559,6 +559,14 @@ module Homebrew
     @default_download_queue ||= T.let(DownloadQueue.new, T.nilable(DownloadQueue))
   end
 
+  sig { void }
+  def self.reset_default_download_queue
+    # Skip `shutdown` for a leaked RSpec double, which cannot receive
+    # messages outside the per-example rspec-mocks lifecycle.
+    @default_download_queue.shutdown if @default_download_queue.is_a?(DownloadQueue)
+    @default_download_queue = nil
+  end
+
   sig { void }
   def self.shutdown_default_download_queue
     @default_download_queue&.shutdown
diff --git a/Library/Homebrew/test/download_queue_spec.rb b/Library/Homebrew/test/download_queue_spec.rb
index 54c0bfc9de..7550103dfd 100644
--- a/Library/Homebrew/test/download_queue_spec.rb
+++ b/Library/Homebrew/test/download_queue_spec.rb
@@ -361,4 +361,24 @@ RSpec.describe Homebrew::DownloadQueue do
     download_queue.enqueue(bottle, check_attestation: true)
     download_queue.fetch
   end
+
+  describe "Homebrew.default_download_queue", order: :defined do
+    it "memoizes the queue created on first use" do
+      queue = instance_double(described_class, shutdown: nil)
+      allow(described_class).to receive(:new).and_return(queue)
+
+      expect(Homebrew.default_download_queue).to be(queue)
+    end
+
+    it "does not leak a queue stubbed by an earlier example" do
+      expect(Homebrew.default_download_queue).to be_an_instance_of(described_class)
+    end
+
+    it "shuts down a memoized real queue when reset" do
+      queue = Homebrew.default_download_queue
+      expect(queue).to receive(:shutdown)
+
+      Homebrew.reset_default_download_queue
+    end
+  end
 end
diff --git a/Library/Homebrew/test/spec_helper.rb b/Library/Homebrew/test/spec_helper.rb
index 2811726f36..6372a3f6a6 100644
--- a/Library/Homebrew/test/spec_helper.rb
+++ b/Library/Homebrew/test/spec_helper.rb
@@ -364,6 +364,10 @@ RSpec.configure do |config|
       ENV.replace(@__env)
       Homebrew::SimulateSystem.clear
       Context.current = Context::ContextStruct.new
+      # Shut down and drop any memoized download queue so an example that
+      # stubbed `DownloadQueue.new` cannot leak a double into later examples
+      # or the `at_exit` shutdown hook.
+      Homebrew.reset_default_download_queue if Homebrew.respond_to?(:reset_default_download_queue)
 
       $stdout.reopen(@__stdout)
       $stderr.reopen(@__stderr)