diff --git a/spade/message.py b/spade/message.py
index 7bfe1967..27c7d047 100644
--- a/spade/message.py
+++ b/spade/message.py
@@ -234,9 +234,10 @@ def prepare(self):
                     )
                 )
 
-            data.fields.append(forms_xso.Field(var="_thread_node",
-                                               type_=forms_xso.FieldType.TEXT_SINGLE,
-                                               values=[self.thread]))
+            if self.thread:
+                data.fields.append(forms_xso.Field(var="_thread_node",
+                                                   type_=forms_xso.FieldType.TEXT_SINGLE,
+                                                   values=[self.thread]))
 
             data.title = SPADE_X_METADATA
             msg.xep0004_data = [data]
diff --git a/tests/test_message.py b/tests/test_message.py
index 5e99556f..8beeee32 100644
--- a/tests/test_message.py
+++ b/tests/test_message.py
@@ -73,6 +73,19 @@ def test_body_with_languages():
     assert new_msg.body == "Hello World"
 
 
+def test_thread_empty():
+    msg = Message(thread=None)
+
+    assert msg.thread is None
+    assert msg.metadata == {}
+
+    aiomsg = msg.prepare()
+    for data in aiomsg.xep0004_data:
+        if data.title == SPADE_X_METADATA:
+            for field in data.fields:
+                assert field.var != "_thread_node"
+
+
 def test_equal(message):
     assert message == copy.copy(message)