diff --git a/src/interfaces.ts b/src/interfaces.ts
index 2c4ed880b..8f2b183ef 100644
--- a/src/interfaces.ts
+++ b/src/interfaces.ts
@@ -139,7 +139,7 @@ export interface WebpackModule {
 }
 
 export interface Watcher {
-    mtimes: number; // a guess
+    getTimes(): { [filePath: string]: number };
 }
 
 export interface WebpackNodeWatchFileSystem {
diff --git a/src/watch-run.ts b/src/watch-run.ts
index ad9169ad6..b5ef698e8 100644
--- a/src/watch-run.ts
+++ b/src/watch-run.ts
@@ -16,7 +16,7 @@ function makeWatchRun(
             instance.modifiedFiles = {};
         }
 
-        Object.keys(watcher.mtimes)
+        Object.keys(watcher.getTimes())
             .filter(filePath => !!filePath.match(constants.tsTsxJsJsxRegex))
             .forEach(filePath => {
                 filePath = path.normalize(filePath);