diff --git a/actionpack/CHANGELOG.md b/actionpack/CHANGELOG.md
index 68cbe847d0b20..be8ec824d5708 100644
--- a/actionpack/CHANGELOG.md
+++ b/actionpack/CHANGELOG.md
@@ -1,3 +1,7 @@
+*   Fix ActionController::Live controller test deadlocks by removing the body buffer size limit for tests.
+
+    *Dylan Thacker-Smith*
+
 *   Drop support for the `SERVER_ADDR` header
 
     Following up https://github.com/rack/rack/pull/1573 and https://github.com/rails/rails/pull/42349
diff --git a/actionpack/lib/action_controller/metal/live.rb b/actionpack/lib/action_controller/metal/live.rb
index 5c684ba173cf3..ca7d3d6382b2e 100644
--- a/actionpack/lib/action_controller/metal/live.rb
+++ b/actionpack/lib/action_controller/metal/live.rb
@@ -127,6 +127,11 @@ class ClientDisconnected < RuntimeError
     class Buffer < ActionDispatch::Response::Buffer #:nodoc:
       include MonitorMixin
 
+      class << self
+        attr_accessor :queue_size
+      end
+      @queue_size = 10
+
       # Ignore that the client has disconnected.
       #
       # If this value is `true`, calling `write` after the client
@@ -136,7 +141,7 @@ class Buffer < ActionDispatch::Response::Buffer #:nodoc:
       attr_accessor :ignore_disconnect
 
       def initialize(response)
-        super(response, SizedQueue.new(10))
+        super(response, build_queue(self.class.queue_size))
         @error_callback = lambda { true }
         @cv = new_cond
         @aborted = false
@@ -219,6 +224,10 @@ def each_chunk(&block)
             yield str
           end
         end
+
+        def build_queue(queue_size)
+          queue_size ? SizedQueue.new(queue_size) : Queue.new
+        end
     end
 
     class Response < ActionDispatch::Response #:nodoc: all
diff --git a/actionpack/lib/action_controller/test_case.rb b/actionpack/lib/action_controller/test_case.rb
index 7c9221e2cef96..c4ff30277eb2a 100644
--- a/actionpack/lib/action_controller/test_case.rb
+++ b/actionpack/lib/action_controller/test_case.rb
@@ -24,6 +24,9 @@ module Live
     def new_controller_thread # :nodoc:
       yield
     end
+
+    # Avoid a deadlock from the queue filling up
+    Buffer.queue_size = nil
   end
 
   # ActionController::TestCase will be deprecated and moved to a gem in the future.
diff --git a/actionpack/test/controller/live_stream_test.rb b/actionpack/test/controller/live_stream_test.rb
index 6d008144ae5f7..2f7606255c283 100644
--- a/actionpack/test/controller/live_stream_test.rb
+++ b/actionpack/test/controller/live_stream_test.rb
@@ -264,6 +264,13 @@ def overfill_buffer_and_die
         end
       end
 
+      def overfill_default_buffer
+        ("a".."z").each do |char|
+          response.stream.write(char)
+        end
+        response.stream.close
+      end
+
       def ignore_client_disconnect
         response.stream.ignore_disconnect = true
 
@@ -368,7 +375,15 @@ def test_async_stream
       assert t.join(3), "timeout expired before the thread terminated"
     end
 
+    def test_infinite_test_buffer
+      get :overfill_default_buffer
+      assert_equal ("a".."z").to_a.join, response.stream.body
+    end
+
     def test_abort_with_full_buffer
+      old_queue_size = ActionController::Live::Buffer.queue_size
+      ActionController::Live::Buffer.queue_size = 10
+
       @controller.latch = Concurrent::CountDownLatch.new
       @controller.error_latch = Concurrent::CountDownLatch.new
 
@@ -389,6 +404,8 @@ def test_abort_with_full_buffer
         @controller.error_latch.wait
         assert_match "Error while streaming", output.rewind && output.read
       end
+    ensure
+      ActionController::Live::Buffer.queue_size = old_queue_size
     end
 
     def test_ignore_client_disconnect