diff --git a/packages/vite/src/node/config.ts b/packages/vite/src/node/config.ts
index 0c46b7f3f68eec..853e15b119de68 100644
--- a/packages/vite/src/node/config.ts
+++ b/packages/vite/src/node/config.ts
@@ -772,6 +772,10 @@ export async function loadConfigFromFile(
     // explicit config path is always resolved from cwd
     resolvedPath = path.resolve(configFile)
     isTS = configFile.endsWith('.ts')
+
+    if (configFile.endsWith('.mjs')) {
+      isMjs = true
+    }
   } else {
     // implicit config file loaded from inline root (if present)
     // otherwise from cwd