diff --git a/lib/builder/builder.js b/lib/builder/builder.js
index 0982b3b7df..970d77ed2a 100644
--- a/lib/builder/builder.js
+++ b/lib/builder/builder.js
@@ -365,8 +365,9 @@ export default class Builder extends Tapable {
     compilersOptions.push(clientConfig)
 
     // Server
-    const serverConfig = serverWebpackConfig.call(this)
+    let serverConfig = null
     if (this.options.build.ssr) {
+      serverConfig = serverWebpackConfig.call(this)
       compilersOptions.push(serverConfig)
     }
 
@@ -380,7 +381,7 @@ export default class Builder extends Tapable {
       }
 
       // Server config
-      if (!serverConfig.resolve.alias[p.name]) {
+      if (serverConfig && !serverConfig.resolve.alias[p.name]) {
         // Alias to noop for ssr:false plugins
         serverConfig.resolve.alias[p.name] = p.ssr ? src : './empty.js'
       }