diff --git a/src/test/errors/args.lua b/src/test/errors/args.lua
index 90f4182f..692bb838 100644
--- a/src/test/errors/args.lua
+++ b/src/test/errors/args.lua
@@ -53,16 +53,19 @@ notatable    = except(sometable)
 notafunction = except(somefunction)
 notanil      = except(somenil)
 
+local structtypes = { 
+	['table']='<table>',
+	['function']='<function>',
+	['thread']='<thread>',
+	['userdata']='<userdata>',
+}
+
 local function signature(name,arglist)
 	local t = {}
 	for i=1,#arglist do
-		if type(arglist[i]) == 'table' then 
-			t[i] = 'table'
-		elseif type(arglist[i]) == 'function' then
-			t[i] = 'function'
-		else
-			t[i] = tostring(arglist[i])
-		end 
+		local ai = arglist[i]
+		local ti = type(ai)
+		t[i] = structtypes[ti] or tostring(ai)
 	end
 	return name..'('..table.concat(t,',')..')'
 end
diff --git a/src/test/errors/coroutinelibargs.lua b/src/test/errors/coroutinelibargs.lua
new file mode 100644
index 00000000..15669002
--- /dev/null
+++ b/src/test/errors/coroutinelibargs.lua
@@ -0,0 +1,43 @@
+package.path = "?.lua;src/test/errors/?.lua"
+require 'args'
+
+-- arg type tests for coroutine library functions
+
+-- coroutine.create
+banner('coroutine.create')
+checkallpass('coroutine.create',{somefunction})
+checkallerrors('coroutine.create',{notafunction},'bad argument')
+
+-- coroutine.resume
+banner('coroutine.resume')
+local co = coroutine.create(function() while true do coroutine.yield() end end)
+checkallpass('coroutine.resume',{{co},anylua})
+checkallerrors('coroutine.resume',{anylua},'bad argument')
+
+-- coroutine.running
+banner('coroutine.running')
+checkallpass('coroutine.running',{anylua})
+
+-- coroutine.status
+banner('coroutine.status')
+checkallpass('coroutine.status',{{co}})
+checkallerrors('coroutine.status',{anylua},'bad argument')
+
+-- coroutine.wrap
+banner('coroutine.wrap')
+checkallpass('coroutine.wrap',{somefunction})
+checkallerrors('coroutine.wrap',{notafunction},'bad argument')
+
+-- coroutine.yield
+banner('coroutine.yield')
+local function f() 
+	print( 'yield', coroutine.yield() )
+	print( 'yield', coroutine.yield(astring) )
+	print( 'yield', coroutine.yield(anumber) )
+	print( 'yield', coroutine.yield(aboolean) )
+end
+local co = coroutine.create( f )
+repeat 
+	print( 'resume', coroutine.resume(co,astring,anumber) )
+until coroutine.status(co) ~= 'suspended'
+