diff --git a/lib/uniword.rb b/lib/uniword.rb
index 16bd59d4..cd8f6f4f 100644
--- a/lib/uniword.rb
+++ b/lib/uniword.rb
@@ -46,10 +46,16 @@ module Uniword
   # directly, falling back to :default for Uniword's own types. Setting
   # Config.default_register means from_xml/to_xml calls without an explicit
   # register: argument use :uniword automatically.
+  #
+  # OmmlIntegration (autoloaded below) then substitutes omml's minimal
+  # WordprocessingML stubs with Uniword's richer classes via the Register's
+  # type substitution mechanism — single source of truth for WordprocessingML.
   require "omml"
   Omml::Configuration.register_in(:uniword)
   Lutaml::Model::Config.default_register = :uniword
 
+  autoload :OmmlIntegration, "uniword/omml_integration"
+
   # Version constant
   autoload :VERSION, "uniword/version"
   autoload :ModelAttributeAccess, "uniword/model_attribute_access"
@@ -344,4 +350,8 @@ def html_to_docx(html, path)
       from_html(html).to_file(path)
     end
   end
+
+  # Register WordprocessingML substitutions after autoloads are declared
+  # so OmmlIntegration can resolve Uniword class constants via const_get.
+  OmmlIntegration.register
 end
diff --git a/lib/uniword/omml_integration.rb b/lib/uniword/omml_integration.rb
new file mode 100644
index 00000000..f1e6dcbb
--- /dev/null
+++ b/lib/uniword/omml_integration.rb
@@ -0,0 +1,62 @@
+# frozen_string_literal: true
+
+require "omml"
+
+module Uniword
+  # Registers Uniword's WordprocessingML classes as substitutions for
+  # Omml::Models' minimal WordprocessingML stubs. When an Omml model
+  # (e.g. CTOMath) resolves a WordprocessingML type symbol (e.g.
+  # +:ct_br+), the Register's substitution table redirects resolution
+  # to the corresponding Uniword class.
+  #
+  # This keeps a single source of truth for WordprocessingML types:
+  # Uniword owns the rich, builder-friendly classes; omml owns the math
+  # schema. The two meet through register substitution, not through
+  # duplicate model definitions.
+  module OmmlIntegration
+    SUBSTITUTIONS = {
+      "Omml::Models::CTBr" => "Uniword::Wordprocessingml::Break",
+    }.freeze
+
+    class << self
+      def register
+        ensure_omml_context
+        register_substitutions
+      end
+
+      private
+
+      def ensure_omml_context
+        return if Lutaml::Model::GlobalContext.context(:uniword)
+
+        Omml::Configuration.register_in(:uniword)
+        Lutaml::Model::Config.default_register = :uniword
+      end
+
+      def register_substitutions
+        register_handle = Lutaml::Model::GlobalRegister.lookup(:uniword)
+        return unless register_handle
+
+        SUBSTITUTIONS.each do |omml_class_name, uniword_class_name|
+          omml_class = constantize(omml_class_name)
+          uniword_class = constantize(uniword_class_name)
+          next unless omml_class && uniword_class
+
+          register_handle.register_global_type_substitution(
+            from_type: omml_class,
+            to_type: uniword_class,
+          )
+        end
+      end
+
+      def constantize(class_name)
+        parts = class_name.split("::")
+        parts.reduce(Object) do |scope, part|
+          scope.const_get(part)
+        end
+      rescue NameError
+        nil
+      end
+    end
+  end
+end