diff --git a/Lib/xml/etree/ElementTree.py b/Lib/xml/etree/ElementTree.py
index ce67d7d7d54748..32a6ecd2dd2d50 100644
--- a/Lib/xml/etree/ElementTree.py
+++ b/Lib/xml/etree/ElementTree.py
@@ -679,6 +679,7 @@ def iterfind(self, path, namespaces=None):
     def write(self, file_or_filename,
               encoding=None,
               xml_declaration=None,
+              xml_declaration_definition='<?xml version="{version}" encoding="{encoding}"?>',
               default_namespace=None,
               method=None, *,
               short_empty_elements=True):
@@ -694,6 +695,14 @@ def write(self, file_or_filename,
                                is added if encoding IS NOT either of:
                                US-ASCII, UTF-8, or Unicode
 
+          *xml_declaration_definition* -- string for customizing encoding declaration
+                                          as documentation always shows doublequotes but
+                                          singlequote where hardcoded here.
+                                          to be rfc conform which allows doublequotes and
+                                          singlequote for declaration. default value is
+                                          switched to doublquotes here to stay on one format.
+                                          placeholders: {version}, {encoding}
+
           *default_namespace* -- sets the default XML namespace (for "xmlns")
 
           *method* -- either "xml" (default), "html, "text", or "c14n"
@@ -719,8 +728,10 @@ def write(self, file_or_filename,
                     (xml_declaration is None and
                      encoding.lower() != "unicode" and
                      declared_encoding.lower() not in ("utf-8", "us-ascii"))):
-                write("<?xml version='1.0' encoding='%s'?>\n" % (
-                    declared_encoding,))
+                # version configuration is'nt necessary, can be overwritten
+                # in declaration_definition at runtime
+                data = {'version':'1.0', 'encoding': declared_encoding}
+                write(xml_declaration_definition.format(**data)+"\n")                         
             if method == "text":
                 _serialize_text(write, self._root)
             else: