diff --git a/Lib/test/test_minidom.py b/Lib/test/test_minidom.py
index a1516c242da..5ab4bfe1a4f 100644
--- a/Lib/test/test_minidom.py
+++ b/Lib/test/test_minidom.py
@@ -1518,6 +1518,10 @@ def testEmptyXMLNSValue(self):
         doc2 = parseString(doc.toxml())
         self.confirm(doc2.namespaceURI == xml.dom.EMPTY_NAMESPACE)
 
+    def testExceptionOnSpacesInXMLNSValue(self):
+        with self.assertRaisesRegex(ValueError, 'Unsupported syntax'):
+            parseString('<element xmlns:abc="http:abc.com/de f g/hi/j k"><abc:foo /></element>')
+
     def testDocRemoveChild(self):
         doc = parse(tstfile)
         title_tag = doc.documentElement.getElementsByTagName("TITLE")[0]
diff --git a/Lib/xml/dom/expatbuilder.py b/Lib/xml/dom/expatbuilder.py
index 81e2df70d7a..89761443406 100644
--- a/Lib/xml/dom/expatbuilder.py
+++ b/Lib/xml/dom/expatbuilder.py
@@ -121,10 +121,12 @@ def _parse_ns_name(builder, name):
         qname = "%s:%s" % (prefix, localname)
         qname = intern(qname, qname)
         localname = intern(localname, localname)
-    else:
+    elif len(parts) == 2:
         uri, localname = parts
         prefix = EMPTY_PREFIX
         qname = localname = intern(localname, localname)
+    else:
+        raise ValueError("Unsupported syntax: spaces in URIs not supported: %r" % name)
     return intern(uri, uri), localname, prefix, qname
 
 
diff --git a/Misc/ACKS b/Misc/ACKS
index e08bb1346e2..7a37df80cfe 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -1257,6 +1257,7 @@ Joel Stanley
 Anthony Starks
 Oliver Steele
 Greg Stein
+Marek Stepniowski
 Baruch Sterin
 Chris Stern
 Alex Stewart
diff --git a/Misc/NEWS b/Misc/NEWS
index 55a146ad83c..e59ba478dbf 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -54,6 +54,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #12220: mindom now raises a custom ValueError indicating it doesn't
+  support spaces in URIs instead of letting a 'split' ValueError bubble up.
+
 - Issue #21068: The ssl.PROTOCOL* constants are now enum members.
 
 - Issue #21262: New method assert_not_called for Mock.