diff --git a/lib/datasource/docker/index.js b/lib/datasource/docker/index.js
index 25e265b530e40a5a8625a1c255361247654ccbce..6a8345323bb60ae3b5ecd4c3ce10ad4b5f309d7c 100644
--- a/lib/datasource/docker/index.js
+++ b/lib/datasource/docker/index.js
@@ -11,16 +11,16 @@ module.exports = {
   getPkgReleases,
 };
 
-function massageRegistry(config, input) {
+function massageRegistry(input, registryUrls) {
   let registry = input;
-  if (!registry && is.nonEmptyArray(config.registryUrls)) {
-    [registry] = config.registryUrls;
+  if (!registry && is.nonEmptyArray(registryUrls)) {
+    [registry] = registryUrls;
   }
   if (!registry || registry === 'docker.io') {
-    registry = 'index.docker.io'; // eslint-disable-line no-param-reassign
+    registry = 'index.docker.io';
   }
   if (!registry.match('$https?://')) {
-    registry = `https://${registry}`; // eslint-disable-line no-param-reassign
+    registry = `https://${registry}`;
   }
   return registry;
 }
@@ -190,7 +190,7 @@ async function getManifestResponse(registry, repository, tag) {
 async function getDigest(config, newValue) {
   const { dockerRegistry, depName } = config;
   logger.debug(`getDigest(${dockerRegistry}, ${depName}, ${newValue})`);
-  const massagedRegistry = massageRegistry(config, dockerRegistry);
+  const massagedRegistry = massageRegistry(dockerRegistry, config.registryUrls);
   const repository = getRepository(depName, dockerRegistry);
   const newTag = newValue || 'latest';
   try {
@@ -317,7 +317,7 @@ async function getTags(registry, repository) {
 async function getPkgReleases(purl, config = {}) {
   const { fullname, qualifiers } = purl;
   const { registry } = qualifiers;
-  const massagedRegistry = massageRegistry(config, registry);
+  const massagedRegistry = massageRegistry(registry, config.registryUrls);
   const repository = getRepository(fullname, registry);
   const tags = await getTags(massagedRegistry, repository);
   if (!tags) {