--- a/spec/util_async_spec.lua	Fri Mar 23 14:18:27 2018 +0000
+++ b/spec/util_async_spec.lua	Fri Mar 23 14:22:01 2018 +0000
@@ -613,23 +613,4 @@
 			assert.spy(r.watchers.error).was_not.called();
 		end);
 	end);
-
-	describe("#once()", function ()
-		it("should work", function ()
-			local f = spy.new(function ()
-				assert.truthy(async.ready());
-			end);
-			async.once(f);
-			assert.spy(f).was.called();
-			assert.spy(f).was.called_with();
-		end);
-		it("should propagate errors", function ()
-			local function should_error()
-				async.once(function ()
-					error("hello world");
-				end);
-			end;
-			assert.error_matches(should_error, "hello world");
-		end);
-	end);
 end);

--- a/util/async.lua	Fri Mar 23 14:18:27 2018 +0000
+++ b/util/async.lua	Fri Mar 23 14:22:01 2018 +0000
@@ -226,20 +226,6 @@
 	return pcall(checkthread);
 end
 
-local once; -- forward declaration
-do
-	local once_watchers = {
-		error = function (_, err)
-			error(err);
-		end;
-	};
-	local function once_runner(func) func(); end
-	function once(func)
-		local r = runner(once_runner, once_watchers);
-		return r:run(func);
-	end
-end
-
 local function sleep(s)
 	local wait, done = waiter();
 	timer.add_task(s, done);