diff --git a/Lib/test/test_xml_etree.py b/Lib/test/test_xml_etree.py
index e802359..08f7988 100644
--- a/Lib/test/test_xml_etree.py
+++ b/Lib/test/test_xml_etree.py
@@ -1119,6 +1119,11 @@
     >>> elem = ET.Element(ET.QName("uri", "tag"))
     >>> serialize(elem) # 1.3
     '<ns0:tag xmlns:ns0="uri" />'
+    >>> elem = ET.Element(ET.QName("uri", "tag"))
+    >>> subelem = ET.SubElement(elem, ET.QName("uri", "tag1"))
+    >>> subelem = ET.SubElement(elem, ET.QName("uri", "tag2"))
+    >>> serialize(elem) # 1.4
+    '<ns0:tag xmlns:ns0="uri"><ns0:tag1 /><ns0:tag2 /></ns0:tag>'
 
     2) decorated attributes
 
diff --git a/Lib/xml/etree/ElementTree.py b/Lib/xml/etree/ElementTree.py
index 9f5717e..75fbea9 100644
--- a/Lib/xml/etree/ElementTree.py
+++ b/Lib/xml/etree/ElementTree.py
@@ -913,8 +913,9 @@
         iterate = elem.getiterator # cET compatibility
     for elem in iterate():
         tag = elem.tag
-        if isinstance(tag, QName) and tag.text not in qnames:
-            add_qname(tag.text)
+        if isinstance(tag, QName):
+            if tag.text not in qnames:
+                add_qname(tag.text)
         elif isinstance(tag, str):
             if tag not in qnames:
                 add_qname(tag)