diff --git a/lib/File-builder.js b/lib/File-builder.js
index 0971a9e..3d9d4e2 100644
--- a/lib/File-builder.js
+++ b/lib/File-builder.js
@@ -39,13 +39,7 @@ class FileBuilder {
     return dirPath
   }
 
-  writeStreamInfo (incomingCsvLine, callback) {
-    this.writeStreamInfoAsync(incomingCsvLine)
-      .then(info => callback(null, info))
-      .catch(err => callback(err))
-  }
-
-  async writeStreamInfoAsync (incomingCsvLine) {
+  async findStreamInfo (incomingCsvLine) {
     const dirPath = this.dirPathFromCsvLine(incomingCsvLine)
     const fileConfig = this.fileConfigFromCsvLine(incomingCsvLine)
     const key = dirPath + '/' + fileConfig.filename + '.csv'
@@ -58,7 +52,7 @@ class FileBuilder {
     this.files[key] = info
 
     return info
-  } // writeStreamInfo
+  } // findStreamInfo
 
   async createWriteStream (key, dirPath, fileConfig) {
     if (this.knownDirs.indexOf(dirPath) === -1) {
diff --git a/lib/Writer.js b/lib/Writer.js
index 1b562a9..9b6d153 100644
--- a/lib/Writer.js
+++ b/lib/Writer.js
@@ -1,4 +1,5 @@
 const Writable = require('stream').Writable
+const writeToStream = require('./write-to-stream')
 
 class FileWriter extends Writable {
   constructor (fileBuilder, options) {
@@ -15,28 +16,26 @@ class FileWriter extends Writable {
   }
 
   _write (incomingCsvLine, encoding, callback) {
+    this.doWrite(incomingCsvLine)
+      .then(() => callback())
+      .catch(err => callback(err))
+  }
+
+  async doWrite (incomingCsvLine) {
     if (!(this.firstLine && this.skipFirstLine)) {
       this.firstLine = false
-      this.fileBuilder.writeStreamInfo(incomingCsvLine, function (err, info) {
-        if (err) {
-          callback(err)
-        } else {
-          info.writeStream.write(info.transformer.transform(incomingCsvLine), function (err) {
-            if (err) {
-              callback(err)
-            } else {
-              info.count += 1
-              callback()
-            }
-          })
-        }
-      })
+
+      const info = await this.fileBuilder.findStreamInfo(incomingCsvLine)
+      await writeToStream(
+        info.writeStream,
+        info.transformer.transform(incomingCsvLine)
+      )
+      info.count += 1
     } else {
       // Skipped this first line
       this.firstLine = false
-      callback()
     }
-  }
-}
+  } // _write
+} // FileWriter
 
 module.exports = FileWriter
diff --git a/lib/write-to-stream.js b/lib/write-to-stream.js
index 603b8c3..0338322 100644
--- a/lib/write-to-stream.js
+++ b/lib/write-to-stream.js
@@ -1,4 +1,4 @@
-async function writeToStream(stream, output) {
+async function writeToStream (stream, output) {
   return new Promise((resolve, reject) => {
     stream.write(
       output,