diff --git a/lib/savon/builder.rb b/lib/savon/builder.rb
index 770949aa..253f4996 100644
--- a/lib/savon/builder.rb
+++ b/lib/savon/builder.rb
@@ -77,7 +77,12 @@ def namespaces_with_globals
     def namespaces
       @namespaces ||= begin
         namespaces = SCHEMA_TYPES.dup
-        namespaces["xmlns:#{namespace_identifier}"] = @globals[:namespace] || @wsdl.namespace
+
+        if namespace_identifier == nil
+          namespaces["xmlns"] = @globals[:namespace] || @wsdl.namespace
+        else
+          namespaces["xmlns:#{namespace_identifier}"] = @globals[:namespace] || @wsdl.namespace
+        end
 
         key = ["xmlns"]
         key << env_namespace if env_namespace && env_namespace != ""
@@ -96,7 +101,9 @@ def header
     end
 
     def namespaced_message_tag
-      if @used_namespaces[[@operation_name.to_s]]
+      if namespace_identifier == nil
+        [message_tag, message_attributes]
+      elsif @used_namespaces[[@operation_name.to_s]]
         [@used_namespaces[[@operation_name.to_s]], message_tag, message_attributes]
       else
         [namespace_identifier, message_tag, message_attributes]
diff --git a/spec/savon/options_spec.rb b/spec/savon/options_spec.rb
index 0a80841d..d902ce6a 100644
--- a/spec/savon/options_spec.rb
+++ b/spec/savon/options_spec.rb
@@ -35,6 +35,14 @@
       expect(response.http.body).to include('xmlns:lol="http://v1_0.ws.auth.order.example.com/"')
       expect(response.http.body).to include("<lol:authenticate></lol:authenticate>")
     end
+
+    it "ignores namespace identifier if it is nil" do
+      client = new_client(:endpoint => @server.url(:repeat), :namespace_identifier => nil)
+      response = client.call(:authenticate, message: {user: 'foo'})
+
+      expect(response.http.body).to include('xmlns="http://v1_0.ws.auth.order.example.com/"')
+      expect(response.http.body).to include("<authenticate><user>foo</user></authenticate>")
+    end
   end
 
   context "global :namespaces" do