diff --git a/pdf.js b/pdf.js
index 0f0bfe397..2ce781105 100644
--- a/pdf.js
+++ b/pdf.js
@@ -112,9 +112,9 @@ var StringStream = (function() {
 })();
 
 var FlateStream = (function() {
-    const codeLenCodeMap = [
+    const codeLenCodeMap = new Uint32Array([
         16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15
-    ];
+    ]);
 
     const lengthDecode = [
         [0,   3],