diff -r 16accac4b2f6 Lib/xml/etree/ElementTree.py
--- a/Lib/xml/etree/ElementTree.py	Wed Dec 16 05:04:29 2015 +0000
+++ b/Lib/xml/etree/ElementTree.py	Wed Dec 16 13:13:08 2015 +0200
@@ -895,33 +895,31 @@ def _namespaces(elem, default_namespace=
 
 def _serialize_xml(write, elem, qnames, namespaces,
                    short_empty_elements, **kwargs):
-    tag = elem.tag
-    text = elem.text
-    if tag is Comment:
-        write("<!--%s-->" % text)
-    elif tag is ProcessingInstruction:
-        write("<?%s?>" % text)
-    else:
-        tag = qnames[tag]
-        if tag is None:
+    def recurse(elem):
+        tag = elem.tag
+        text = elem.text
+        if tag is Comment:
+            write("<!--%s-->" % text)
+        elif tag is ProcessingInstruction:
+            write("<?%s?>" % text)
+        elif tag is None:
             if text:
                 write(_escape_cdata(text))
             for e in elem:
-                _serialize_xml(write, e, qnames, None,
-                               short_empty_elements=short_empty_elements)
+                recurse(e)
         else:
+            tag = qnames[tag]
             write("<" + tag)
             items = list(elem.items())
-            if items or namespaces:
-                if namespaces:
-                    for v, k in sorted(namespaces.items(),
-                                       key=lambda x: x[1]):  # sort on prefix
-                        if k:
-                            k = ":" + k
-                        write(" xmlns%s=\"%s\"" % (
-                            k,
-                            _escape_attrib(v)
-                            ))
+            nonlocal namespaces
+            if namespaces:
+                for v, k in sorted(namespaces.items(),
+                                   key=lambda x: x[1]):  # sort on prefix
+                    if k:
+                        k = ":" + k
+                    write(' xmlns%s="%s"' % (k, _escape_attrib(v)))
+                namespaces = None
+            if items:
                 for k, v in sorted(items):  # lexical order
                     if isinstance(k, QName):
                         k = k.text
@@ -929,19 +927,20 @@ def _serialize_xml(write, elem, qnames, 
                         v = qnames[v.text]
                     else:
                         v = _escape_attrib(v)
-                    write(" %s=\"%s\"" % (qnames[k], v))
+                    write(' %s="%s"' % (qnames[k], v))
             if text or len(elem) or not short_empty_elements:
                 write(">")
                 if text:
                     write(_escape_cdata(text))
                 for e in elem:
-                    _serialize_xml(write, e, qnames, None,
-                                   short_empty_elements=short_empty_elements)
+                    recurse(e)
                 write("</" + tag + ">")
             else:
                 write(" />")
-    if elem.tail:
-        write(_escape_cdata(elem.tail))
+        if elem.tail:
+            write(_escape_cdata(elem.tail))
+
+    return recurse(elem)
 
 HTML_EMPTY = ("area", "base", "basefont", "br", "col", "frame", "hr",
               "img", "input", "isindex", "link", "meta", "param")
@@ -952,32 +951,31 @@ except NameError:
     pass
 
 def _serialize_html(write, elem, qnames, namespaces, **kwargs):
-    tag = elem.tag
-    text = elem.text
-    if tag is Comment:
-        write("<!--%s-->" % _escape_cdata(text))
-    elif tag is ProcessingInstruction:
-        write("<?%s?>" % _escape_cdata(text))
-    else:
-        tag = qnames[tag]
-        if tag is None:
+    def recurse(elem):
+        tag = elem.tag
+        text = elem.text
+        if tag is Comment:
+            write("<!--%s-->" % _escape_cdata(text))
+        elif tag is ProcessingInstruction:
+            write("<?%s?>" % _escape_cdata(text))
+        elif tag is None:
             if text:
                 write(_escape_cdata(text))
             for e in elem:
-                _serialize_html(write, e, qnames, None)
+                recurse(e)
         else:
+            tag = qnames[tag]
             write("<" + tag)
             items = list(elem.items())
-            if items or namespaces:
-                if namespaces:
-                    for v, k in sorted(namespaces.items(),
-                                       key=lambda x: x[1]):  # sort on prefix
-                        if k:
-                            k = ":" + k
-                        write(" xmlns%s=\"%s\"" % (
-                            k,
-                            _escape_attrib(v)
-                            ))
+            nonlocal namespaces
+            if namespaces:
+                for v, k in sorted(namespaces.items(),
+                                   key=lambda x: x[1]):  # sort on prefix
+                    if k:
+                        k = ":" + k
+                    write(' xmlns%s="%s"' % (k, _escape_attrib_html(v)))
+                namespaces = None
+            if items:
                 for k, v in sorted(items):  # lexical order
                     if isinstance(k, QName):
                         k = k.text
@@ -986,7 +984,7 @@ def _serialize_html(write, elem, qnames,
                     else:
                         v = _escape_attrib_html(v)
                     # FIXME: handle boolean attributes
-                    write(" %s=\"%s\"" % (qnames[k], v))
+                    write(' %s="%s"' % (qnames[k], v))
             write(">")
             ltag = tag.lower()
             if text:
@@ -995,11 +993,13 @@ def _serialize_html(write, elem, qnames,
                 else:
                     write(_escape_cdata(text))
             for e in elem:
-                _serialize_html(write, e, qnames, None)
+                recurse(e)
             if ltag not in HTML_EMPTY:
                 write("</" + tag + ">")
-    if elem.tail:
-        write(_escape_cdata(elem.tail))
+        if elem.tail:
+            write(_escape_cdata(elem.tail))
+
+    return recurse(elem)
 
 def _serialize_text(write, elem):
     for part in elem.itertext():