diff --git a/lib/oga/xml/tree_builder.rb b/lib/oga/xml/tree_builder.rb
index 92877d3..0805e39 100644
--- a/lib/oga/xml/tree_builder.rb
+++ b/lib/oga/xml/tree_builder.rb
@@ -120,6 +120,11 @@ module Oga
         return *node
       end
 
+      ##
+      # Raises for every unhandled node.
+      #
+      # @param [Oga::AST::Node] node
+      #
       def handler_missing(node)
         raise "No handler for node type #{node.type.inspect}"
       end
diff --git a/spec/oga/xml/tree_builder_spec.rb b/spec/oga/xml/tree_builder_spec.rb
index d4eafa8..0e6323c 100644
--- a/spec/oga/xml/tree_builder_spec.rb
+++ b/spec/oga/xml/tree_builder_spec.rb
@@ -228,4 +228,15 @@ describe Oga::XML::TreeBuilder do
       @builder.process(s(:attributes)).should == {}
     end
   end
+
+  context '#handler_missing' do
+    before do
+      @node = s(:foo, 'bar')
+    end
+
+    example 'raise when processing an unknown node' do
+      lambda { @builder.process(@node) }
+        .should raise_error('No handler for node type :foo')
+    end
+  end
 end