diff --git a/changelog/344.bugfix b/changelog/344.bugfix
new file mode 100644
index 0000000..a88fca2
--- /dev/null
+++ b/changelog/344.bugfix
@@ -0,0 +1 @@
+Fix issue where Warnings could cause pytest to fail if they do not set the args attribute correctly.
diff --git a/testing/acceptance_test.py b/testing/acceptance_test.py
index dcf717d..987dbe6 100644
--- a/testing/acceptance_test.py
+++ b/testing/acceptance_test.py
@@ -429,6 +429,35 @@ class TestTerminalReporting:
         result = testdir.runpytest(n)
         result.stdout.fnmatch_lines(["*this is a warning*", "*1 passed, 1 warnings*"])
 
+    @pytest.mark.parametrize("n", ["-n0", "-n1"])
+    def test_custom_subclass(self, testdir, n):
+        """Check that warning subclasses that don't honor the args attribute don't break
+        pytest-xdist (#344)
+        """
+        from pkg_resources import parse_version
+
+        if parse_version(pytest.__version__) < parse_version("3.1"):
+            pytest.skip("pytest warnings requires >= 3.1")
+
+        testdir.makepyfile(
+            """
+            import warnings, py, pytest
+
+            class MyWarning(UserWarning):
+
+                def __init__(self, p1, p2):
+                    self.p1 = p1
+                    self.p2 = p2
+                    self.args = ()
+
+            def test_func(request):
+                warnings.warn(MyWarning("foo", 1))
+        """
+        )
+        testdir.syspathinsert()
+        result = testdir.runpytest(n)
+        result.stdout.fnmatch_lines(["*MyWarning*", "*1 passed, 1 warnings*"])
+
     def test_logfinish_hook(self, testdir):
         """Ensure the pytest_runtest_logfinish hook is being properly handled"""
         from _pytest import hookspec
diff --git a/xdist/remote.py b/xdist/remote.py
index 091bde8..bee3471 100644
--- a/xdist/remote.py
+++ b/xdist/remote.py
@@ -182,7 +182,7 @@ def serialize_warning_message(warning_message):
         message_module = type(warning_message.message).__module__
         message_class_name = type(warning_message.message).__name__
         message_args = warning_message.message.args
-        message_str = None
+        message_str = str(warning_message.message)
     else:
         message_str = warning_message.message
         message_module = None
diff --git a/xdist/workermanage.py b/xdist/workermanage.py
index b607d4e..9eb6418 100644
--- a/xdist/workermanage.py
+++ b/xdist/workermanage.py
@@ -426,7 +426,15 @@ def unserialize_warning_message(data):
     if data["message_module"]:
         mod = importlib.import_module(data["message_module"])
         cls = getattr(mod, data["message_class_name"])
-        message = cls(*data["message_args"])
+        try:
+            message = cls(*data["message_args"])
+        except TypeError:
+            message_text = "{mod}.{cls}: {msg}".format(
+                mod=data["message_module"],
+                cls=data["message_class_name"],
+                msg=data["message_str"],
+            )
+            message = Warning(message_text)
     else:
         message = data["message_str"]