diff --git a/lib/string_decoder.js b/lib/string_decoder.js
index fec30beb0a15d4..7df50eb0178377 100644
--- a/lib/string_decoder.js
+++ b/lib/string_decoder.js
@@ -57,7 +57,7 @@ function normalizeEncoding(enc) {
 }
 
 const encodingsMap = {};
-for (var i = 0; i < encodings.length; ++i)
+for (let i = 0; i < encodings.length; ++i)
   encodingsMap[encodings[i]] = i;
 
 // StringDecoder provides an interface for efficiently splitting a series of