diff --git a/src/js/utils.js b/src/js/utils.js
index 728b3ee74..ee04159d7 100644
--- a/src/js/utils.js
+++ b/src/js/utils.js
@@ -544,7 +544,7 @@
     }
 
     encode(arrbuf, arrlen) {
-        const inputLength = arrlen >>> 2;
+        const inputLength = (arrlen + 3) >>> 2;
         const inbuf = new Uint32Array(arrbuf, 0, inputLength);
         const outputLength = this.magic.length + 7 + inputLength * 7;
         const outbuf = new Uint8Array(outputLength);