diff --git a/lib/preprocessor.js b/lib/preprocessor.js
index 05af99c34..3018dd2ee 100644
--- a/lib/preprocessor.js
+++ b/lib/preprocessor.js
@@ -70,63 +70,46 @@ async function runProcessors (preprocessors, file, content) {
   file.sha = CryptoUtils.sha1(content)
 }
 
-function createPriorityPreprocessor (config, preprocessorPriority, basePath, injector) {
+function createPriorityPreprocessor (config = {}, preprocessorPriority, basePath, injector) {
   const emitter = injector.get('emitter')
-  const alreadyDisplayedErrors = {}
-  const instances = {}
-  let patterns = Object.keys(config)
+  const instances = new Map()
 
   function instantiatePreprocessor (name) {
-    if (alreadyDisplayedErrors[name]) {
-      return
-    }
-
-    let p = instances[name]
-    if (p) {
-      return p
+    if (instances.has(name)) {
+      return instances.get(name)
     }
 
+    let p
     try {
       p = injector.get('preprocessor:' + name)
+      if (!p) {
+        log.error(`Failed to instantiate preprocessor ${name}`)
+        emitter.emit('load_error', 'preprocessor', name)
+      }
     } catch (e) {
       if (e.message.includes(`No provider for "preprocessor:${name}"`)) {
         log.error(`Can not load "${name}", it is not registered!\n  Perhaps you are missing some plugin?`)
       } else {
         log.error(`Can not load "${name}"!\n  ` + e.stack)
       }
-      alreadyDisplayedErrors[name] = true
-      emitter.emit('load_error', 'preprocessor', name)
-    }
-
-    if (!p && !alreadyDisplayedErrors[name]) {
-      alreadyDisplayedErrors[name] = true
-      log.error(`Failed to instantiate preprocessor ${name}`)
       emitter.emit('load_error', 'preprocessor', name)
-    } else {
-      instances[name] = p
     }
 
+    instances.set(name, p)
     return p
   }
-
-  let allPreprocessors = []
-  patterns.forEach((pattern) => {
-    allPreprocessors = _.union(allPreprocessors, config[pattern])
-  })
-  allPreprocessors.forEach(instantiatePreprocessor)
+  _.union.apply(_, Object.values(config)).forEach(instantiatePreprocessor)
 
   return async function preprocess (file) {
-    patterns = Object.keys(config)
-
     const buffer = await tryToRead(file.originalPath, log)
     const isBinary = await isBinaryFile(buffer, buffer.length)
 
-    let preprocessorNames = []
-    patterns.forEach((pattern) => {
+    const preprocessorNames = Object.keys(config).reduce((res, pattern) => {
       if (mm(file.originalPath, pattern, { dot: true })) {
-        preprocessorNames = _.union(preprocessorNames, config[pattern])
+        res = _.union(res, config[pattern])
       }
-    })
+      return res
+    }, [])
 
     // Apply preprocessor priority.
     const preprocessors = preprocessorNames