diff --git a/packages/builder/src/builder.js b/packages/builder/src/builder.js
index 9a1b35171a..1e1ca70897 100644
--- a/packages/builder/src/builder.js
+++ b/packages/builder/src/builder.js
@@ -29,7 +29,8 @@ import {
   relativeTo,
   waitFor,
   determineGlobals,
-  stripWhitespace
+  stripWhitespace,
+  isString
 } from '@nuxt/common'
 
 const glob = pify(Glob)
@@ -372,7 +373,7 @@ export default class Builder {
           custom: customFileExists
         }
       })
-      .filter(i => !!i)
+      .filter(Boolean)
 
     // -- Custom templates --
     // Add custom template files
@@ -524,7 +525,7 @@ export default class Builder {
   watchServer() {
     const nuxtRestartWatch = concat(
       this.options.serverMiddleware
-        .filter(i => typeof i === 'string')
+        .filter(isString)
         .map(this.nuxt.resolver.resolveAlias),
       this.options.watch.map(this.nuxt.resolver.resolveAlias),
       path.join(this.options.rootDir, 'nuxt.config.js')
diff --git a/packages/webpack/src/config/utils/postcss.js b/packages/webpack/src/config/utils/postcss.js
index 51674bbad7..0d011ecc0c 100644
--- a/packages/webpack/src/config/utils/postcss.js
+++ b/packages/webpack/src/config/utils/postcss.js
@@ -99,7 +99,7 @@ export default class PostcssConfig {
           const instance = plugin(opts)
           return instance
         })
-        .filter(e => e)
+        .filter(Boolean)
     }
   }