diff --git a/lib/manager/npm/post-update/index.js b/lib/manager/npm/post-update/index.js
index 21662afe8c870c84e4d067111c21745736344e2c..0afee7daf16d8a31282931d7ad29ca8ddc06e4f3 100644
--- a/lib/manager/npm/post-update/index.js
+++ b/lib/manager/npm/post-update/index.js
@@ -206,14 +206,16 @@ async function writeExistingFiles(config, packageFiles) {
           logger.info(`Removing ${widens} from ${npmLock} to force an update`);
           try {
             const npmLockParsed = JSON.parse(existingNpmLock);
-            widens.forEach(depName => {
-              delete npmLockParsed.dependencies[depName];
-            });
+            if (npmLockParsed.dependencies) {
+              widens.forEach(depName => {
+                delete npmLockParsed.dependencies[depName];
+              });
+            }
             existingNpmLock = JSON.stringify(npmLockParsed, null, 2);
           } catch (err) {
             logger.warn(
               { npmLock },
-              'Error massing package-lock.json for widen'
+              'Error massaging package-lock.json for widen'
             );
           }
         }