diff --git a/lib/c14n-canonicalization.js b/lib/c14n-canonicalization.js
index ac533481..9d0419b4 100644
--- a/lib/c14n-canonicalization.js
+++ b/lib/c14n-canonicalization.js
@@ -208,7 +208,12 @@ C14nCanonicalization.prototype.process = function(node, options) {
   var defaultNsForPrefix = options.defaultNsForPrefix || {};
   var ancestorNamespaces = options.ancestorNamespaces || [];
 
-  var res = this.processInner(node, [], defaultNs, defaultNsForPrefix, ancestorNamespaces);
+  var prefixesInScope = [];
+  for (var i = 0; i < ancestorNamespaces.length; i++) {
+    prefixesInScope.push(ancestorNamespaces[i].prefix);
+  }
+
+  var res = this.processInner(node, prefixesInScope, defaultNs, defaultNsForPrefix, ancestorNamespaces);
   return res;
 };
 
diff --git a/test/c14n-non-exclusive-unit-test.js b/test/c14n-non-exclusive-unit-test.js
index 49c837b8..e4a45e22 100644
--- a/test/c14n-non-exclusive-unit-test.js
+++ b/test/c14n-non-exclusive-unit-test.js
@@ -176,3 +176,11 @@ exports["C14n: Don't redeclare an attribute's namespace prefix if already in sco
 
   test_C14nCanonicalization(test, xml, xpath, expected);
 }
+
+exports["C14n: Don't declare an attribute's namespace prefix if in scope from parent"] = function(test) {
+  var xml = "<root xmlns:aaa='bbb'><child1><child2><child3 aaa:foo='bar'></child3></child2></child1></root>"
+  var xpath = "/root/child1";
+  var expected = '<child1 xmlns:aaa="bbb"><child2><child3 aaa:foo="bar"></child3></child2></child1>';
+
+  test_C14nCanonicalization(test, xml, xpath, expected);
+}