diff --git a/packages/transformers/postcss/src/loadConfig.js b/packages/transformers/postcss/src/loadConfig.js
index c2dd54fb41f..48cce81b222 100644
--- a/packages/transformers/postcss/src/loadConfig.js
+++ b/packages/transformers/postcss/src/loadConfig.js
@@ -104,6 +104,10 @@ export async function load({
   options: PluginOptions,
   logger: PluginLogger,
 |}): Promise<?ConfigResult> {
+  if (!config.isSource) {
+    return;
+  }
+
   let configFile: any = await config.getConfig(
     ['.postcssrc', '.postcssrc.json', '.postcssrc.js', 'postcss.config.js'],
     {packageKey: 'postcss'},
diff --git a/packages/transformers/posthtml/src/PostHTMLTransformer.js b/packages/transformers/posthtml/src/PostHTMLTransformer.js
index c2d81d78b36..fa7c11f9323 100644
--- a/packages/transformers/posthtml/src/PostHTMLTransformer.js
+++ b/packages/transformers/posthtml/src/PostHTMLTransformer.js
@@ -13,6 +13,10 @@ import loadPlugins from './loadPlugins';
 
 export default (new Transformer({
   async loadConfig({config, options, logger}) {
+    if (!config.isSource) {
+      return;
+    }
+
     let configFile = await config.getConfig(
       ['.posthtmlrc', '.posthtmlrc.js', 'posthtml.config.js'],
       {