diff --git a/CHANGES.txt b/CHANGES.txt
index e84e069f..fa79f2b1 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -4,7 +4,9 @@ Changelog
 4.2.15 (unreleased)
 -------------------
 
-- Nothing changed yet.
+- Always wrap contents of zcml-additional with a <configure /> node.
+  This makes it possible to use += assignments with zcml-additional.
+  [lgraf]
 
 
 4.2.14 (2014-03-02)
diff --git a/src/plone/recipe/zope2instance/__init__.py b/src/plone/recipe/zope2instance/__init__.py
index 8524bf7d..a0b31e57 100644
--- a/src/plone/recipe/zope2instance/__init__.py
+++ b/src/plone/recipe/zope2instance/__init__.py
@@ -677,6 +677,7 @@ def build_package_includes(self):
                     os.mkdir(includes_path)
 
         if additional_zcml:
+            additional_zcml = additional_zcml_template % additional_zcml
             path=os.path.join(includes_path, "999-additional-overrides.zcml")
             open(path, "w").write(additional_zcml.strip())
 
@@ -1019,3 +1020,10 @@ def render_file_storage(self, file_storage, blob_storage,
     <i18n:registerTranslations directory="%(directory)s" />
 </configure>
 """
+
+# Template used for additional ZCML
+additional_zcml_template = """\
+<configure xmlns="http://namespaces.zope.org/zope">
+    %s
+</configure>
+"""
\ No newline at end of file