diff --git a/lib/protobuf-decoder/varintUtils.js b/lib/protobuf-decoder/varintUtils.js
index 6b9b6b4..9a5bfad 100644
--- a/lib/protobuf-decoder/varintUtils.js
+++ b/lib/protobuf-decoder/varintUtils.js
@@ -1,5 +1,5 @@
 export function decodeVarint(buffer, offset) {
-  let res = this.BigInt(0);
+  let res = 0;
   let shift = 0;
   let byte = 0;
 
@@ -10,8 +10,8 @@ export function decodeVarint(buffer, offset) {
 
     byte = buffer[offset++];
 
-    const multiplier = this.BigInt(2) ** this.BigInt(shift);
-    const thisByteValue = this.BigInt(byte & 0x7f) * multiplier;
+    const multiplier = 2 ** shift;
+    const thisByteValue = (byte & 0x7f) * multiplier;
     shift += 7;
     res = res + thisByteValue;
   } while (byte >= 0x80);