diff --git a/lib/manager/npm/monorepos.js b/lib/manager/npm/monorepos.js
index 56e9c9ed8e6cd9d665e8e0f84442b0a03a8f9c6c..29135456879540f0c487cfe76e337d3642aab214 100644
--- a/lib/manager/npm/monorepos.js
+++ b/lib/manager/npm/monorepos.js
@@ -65,7 +65,10 @@ async function checkMonorepos(config) {
   if (await platform.getFile('package-lock.json')) {
     logger.debug('lerna has a package-lock.json');
     lernaLockFile = 'npm';
-  } else if (await platform.getFile('yarn.lock')) {
+  } else if (
+    lernaJson.npmClient === 'yarn' &&
+    (await platform.getFile('yarn.lock'))
+  ) {
     logger.debug('lerna has non-workspaces yarn');
     lernaLockFile = 'yarn';
   }