diff --git a/packages/gatsby-source-wordpress/README.md b/packages/gatsby-source-wordpress/README.md
index 7df4ad53ad00c..64e23b4a4b734 100644
--- a/packages/gatsby-source-wordpress/README.md
+++ b/packages/gatsby-source-wordpress/README.md
@@ -97,6 +97,10 @@ plugins: [
       // Example:  `["/*/*/comments", "/yoast/**"]` will exclude routes ending in `comments` and
       // all routes that begin with `yoast` from fetch.
       excludedRoutes: ["/*/*/comments", "/yoast/**"],
+      // use a custom normalizer which is applied after the built-in ones.
+      normalizer: function({ entities }) {
+        return entities;
+      },
     },
   },
 ];
@@ -503,6 +507,55 @@ To learn more about image processing check
 * documentation of [gatsby-plugin-sharp](/packages/gatsby-plugin-sharp/),
 * source code of [image processing example
   site](https://github.com/gatsbyjs/gatsby/tree/master/examples/image-processing).
+  
+### Using a custom normalizer
+
+The plugin uses the concept of normalizers to transform the json data from WordPress into 
+GraphQL nodes. You can extend the normalizers by passing a custom function to your `gatsby-config.js`.
+
+#### Example:
+
+You have a custom post type `movie` and a related custom taxonomy `genre` in your WordPress site. Since 
+`gatsby-source-wordpress` doesn't know about the relation of the two, we can build an additional normalizer function to map the movie GraphQL nodes to the genre nodes: 
+
+```javascript
+function mapMoviesToGenres({ entities }) {
+  const genres = entities.filter(e => e.__type === `wordpress__wp_genre`);
+
+  return entities.map(e => {
+    if (e.__type === `wordpress__wp_movie`) {
+      let hasGenres = e.genres && Array.isArray(e.genres) && e.categories.length;
+      // Replace genres with links to their nodes.
+      if (hasGenres) {
+        e.genres___NODE = e.genres.map(c => genres.find(gObj => c === gObj.wordpress_id).id);
+        delete e.genres;
+      }
+    }
+    return e;
+  });
+  
+  return entities;
+}
+```
+
+In your `gatsby-config.js` you can then pass the function to the plugin options:
+
+```javascript
+module.exports = {
+  plugins: [
+    {
+      resolve: 'gatsby-source-wordpress',
+      options: {
+        // ...
+        normalizer: mapMoviesToGenres,
+      },
+    },
+  ],
+};
+```
+
+Next to the entities, the object passed to the custom normalizer function also contains other helpful Gatsby functions 
+and also your `wordpress-source-plugin` options from `gatsby-config.js`. To learn more about the passed object see the [source code](https://github.com/gatsbyjs/gatsby/tree/master/packages/gatsby-source-wordpress/src/gatsby-node.js).
 
 ## Site's `gatsby-node.js` example
 
diff --git a/packages/gatsby-source-wordpress/src/gatsby-node.js b/packages/gatsby-source-wordpress/src/gatsby-node.js
index 98a9695592872..196e7824846b8 100644
--- a/packages/gatsby-source-wordpress/src/gatsby-node.js
+++ b/packages/gatsby-source-wordpress/src/gatsby-node.js
@@ -18,6 +18,7 @@ let _auth
 let _perPage
 let _concurrentRequests
 let _excludedRoutes
+let _normalizer
 
 exports.sourceNodes = async (
   { boundActionCreators, getNode, store, cache, createNodeId },
@@ -32,6 +33,7 @@ exports.sourceNodes = async (
     searchAndReplaceContentUrls = {},
     concurrentRequests = 10,
     excludedRoutes = [],
+    normalizer,
   }
 ) => {
   const { createNode, touchNode } = boundActionCreators
@@ -43,6 +45,7 @@ exports.sourceNodes = async (
   _perPage = perPage
   _concurrentRequests = concurrentRequests
   _excludedRoutes = excludedRoutes
+  _normalizer = normalizer
 
   let entities = await fetch({
     baseUrl,
@@ -112,6 +115,32 @@ exports.sourceNodes = async (
     searchAndReplaceContentUrls,
   })
 
+  // apply custom normalizer
+  if (typeof _normalizer === `function`) {
+    entities = _normalizer({
+      entities,
+      store,
+      cache,
+      createNode,
+      createNodeId,
+      touchNode,
+      getNode,
+      typePrefix,
+      refactoredEntityTypes,
+      baseUrl,
+      protocol,
+      _siteURL,
+      hostingWPCOM,
+      useACF,
+      auth,
+      verboseOutput,
+      perPage,
+      searchAndReplaceContentUrls,
+      concurrentRequests,
+      excludedRoutes,
+    })
+  }
+
   // creates nodes for each entry
   normalize.createNodesFromEntities({ entities, createNode })