diff --git a/lib/oga/xml/element.rb b/lib/oga/xml/element.rb
index bfc7907..2d990c6 100644
--- a/lib/oga/xml/element.rb
+++ b/lib/oga/xml/element.rb
@@ -273,7 +273,7 @@ module Oga
       # @return [Hash]
       #
       def available_namespaces
-        merged = namespaces
+        merged = namespaces.dup
         node   = parent
 
         while node && node.respond_to?(:namespaces)
diff --git a/spec/oga/xml/element_spec.rb b/spec/oga/xml/element_spec.rb
index 3d6ee54..44c51c3 100644
--- a/spec/oga/xml/element_spec.rb
+++ b/spec/oga/xml/element_spec.rb
@@ -418,6 +418,10 @@ describe Oga::XML::Element do
     example 'return the "baz" namespace for the parent' do
       @parent_ns['baz'].uri.should == 'yyy'
     end
+
+    example 'do not modify the list of direct namespaces' do
+      @child.namespaces.key?('foo').should == false
+    end
   end
 
   context '#self_closing?' do