diff --git a/lib/manager/npm/extract/index.ts b/lib/manager/npm/extract/index.ts
index ad22069b05061b7880e4de900d151e7da579c823..277487a440c4e697c93d6ce2a9ac1deb0d9ce872 100644
--- a/lib/manager/npm/extract/index.ts
+++ b/lib/manager/npm/extract/index.ts
@@ -102,11 +102,11 @@ export async function extractPackageFile(
     await deleteLocalFile(npmrcFileName);
   } else {
     npmrc = await readLocalFile(npmrcFileName, 'utf8');
-    if (npmrc?.includes('package-lock')) {
-      logger.debug('Stripping package-lock setting from npmrc');
-      npmrc = npmrc.replace(/(^|\n)package-lock.*?(\n|$)/g, '\n');
-    }
     if (is.string(npmrc)) {
+      if (npmrc.includes('package-lock')) {
+        logger.debug('Stripping package-lock setting from npmrc');
+        npmrc = npmrc.replace(/(^|\n)package-lock.*?(\n|$)/g, '\n');
+      }
       if (npmrc.includes('=${') && getAdminConfig().trustLevel !== 'high') {
         logger.debug('Discarding .npmrc file with variables');
         ignoreNpmrcFile = true;