diff --git a/src/encoder.ts b/src/encoder.ts
index 411f6e3..635a5c9 100644
--- a/src/encoder.ts
+++ b/src/encoder.ts
@@ -15,8 +15,8 @@ function encode6bit(b: number) {
 
 function encode3bytes(b1: number, b2: number, b3: number) {
   return encode6bit((b1 >> 2) & 0x3f).concat(
-    encode6bit(((b1 & 0x3) << 4) | ((b2 >> 4) & 0x3f)),
-    encode6bit(((b2 & 0xf) << 2) | ((b3 >> 6) & 0x3f)),
+    encode6bit((((b1 & 0x3) << 4) | (b2 >> 4)) & 0x3f),
+    encode6bit((((b2 & 0xf) << 2) | (b3 >> 6)) & 0x3f),
     encode6bit(b3 & 0x3f),
   );
 }