diff --git a/src/main/java/org/apache/xml/security/utils/Encryption11ElementProxy.java b/src/main/java/org/apache/xml/security/utils/Encryption11ElementProxy.java
index ba9f6e394..41fb2d50c 100644
--- a/src/main/java/org/apache/xml/security/utils/Encryption11ElementProxy.java
+++ b/src/main/java/org/apache/xml/security/utils/Encryption11ElementProxy.java
@@ -43,7 +43,7 @@ public Encryption11ElementProxy(Document doc) {
         setElement(XMLUtils.createElementInEncryption11Space(doc, this.getBaseLocalName()));
         String prefix = ElementProxy.getDefaultPrefix(this.getBaseNamespace());
         if (prefix != null && prefix.length() > 0) {
-            getElement().setAttribute("xmlns:" + prefix, this.getBaseNamespace());
+            getElement().setAttributeNS(Constants.NamespaceSpecNS, "xmlns:" + prefix, this.getBaseNamespace());
         }
     }
 
diff --git a/src/main/java/org/apache/xml/security/utils/EncryptionElementProxy.java b/src/main/java/org/apache/xml/security/utils/EncryptionElementProxy.java
index c23b33d75..b1b2b907c 100644
--- a/src/main/java/org/apache/xml/security/utils/EncryptionElementProxy.java
+++ b/src/main/java/org/apache/xml/security/utils/EncryptionElementProxy.java
@@ -44,7 +44,7 @@ public EncryptionElementProxy(Document doc) {
         setElement(XMLUtils.createElementInEncryptionSpace(doc, this.getBaseLocalName()));
         String prefix = ElementProxy.getDefaultPrefix(this.getBaseNamespace());
         if (prefix != null && !prefix.isEmpty()) {
-            getElement().setAttribute("xmlns:" + prefix, this.getBaseNamespace());
+            getElement().setAttributeNS(Constants.NamespaceSpecNS, "xmlns:" + prefix, this.getBaseNamespace());
         }
     }
 
diff --git a/src/test/java/org/apache/xml/security/test/dom/encryption/XMLEncryption11Test.java b/src/test/java/org/apache/xml/security/test/dom/encryption/XMLEncryption11Test.java
index d47d0551d..08de39ca3 100644
--- a/src/test/java/org/apache/xml/security/test/dom/encryption/XMLEncryption11Test.java
+++ b/src/test/java/org/apache/xml/security/test/dom/encryption/XMLEncryption11Test.java
@@ -525,6 +525,12 @@ void testAgreementKeyEncryptDecryptDocument(String w3cTag,
         Files.write(Path.of("target","test-enc-"+w3cTag+".xml"), toString(doc.getFirstChild()).getBytes());
         // XMLUtils.outputDOM(doc.getFirstChild(), System.out);
 
+        // re-read the document and compare both are the same after canonicalization
+        Document doc2 = XMLUtils.read(
+                new ByteArrayInputStream(toString(doc.getFirstChild()).getBytes(java.nio.charset.StandardCharsets.UTF_8)),
+                false);
+        assertEquals(toString(doc.getFirstChild()), toString(doc2.getFirstChild()));
+
         // Perform decryption
         Document dd = decryptElement(doc, ecKey, (X509Certificate)cert);
         // XMLUtils.outputDOM(dd.getFirstChild(), System.out);