diff --git a/fallback.js b/fallback.js
index 1d77a9e..c493d49 100644
--- a/fallback.js
+++ b/fallback.js
@@ -9,12 +9,12 @@
  * @return {Boolean} `true` if `buf` contains only correct UTF-8, else `false`
  * @public
  */
-const isValidUTF8 = (buf) => {
-  var len = buf.length;
-  var i = 0;
+function isValidUTF8(buf) {
+  const len = buf.length;
+  let i = 0;
 
   while (i < len) {
-    if (buf[i] < 0x80) {  // 0xxxxxxx
+    if ((buf[i] & 0x80) === 0x00) {  // 0xxxxxxx
       i++;
     } else if ((buf[i] & 0xe0) === 0xc0) {  // 110xxxxx 10xxxxxx
       if (
@@ -23,21 +23,21 @@ const isValidUTF8 = (buf) => {
         (buf[i] & 0xfe) === 0xc0  // overlong
       ) {
         return false;
-      } else {
-        i += 2;
       }
+
+      i += 2;
     } else if ((buf[i] & 0xf0) === 0xe0) {  // 1110xxxx 10xxxxxx 10xxxxxx
       if (
         i + 2 >= len ||
         (buf[i + 1] & 0xc0) !== 0x80 ||
         (buf[i + 2] & 0xc0) !== 0x80 ||
         buf[i] === 0xe0 && (buf[i + 1] & 0xe0) === 0x80 ||  // overlong
-        buf[i] === 0xed && (buf[i + 1] & 0xe0) === 0xa0     // surrogate (U+D800 - U+DFFF)
+        buf[i] === 0xed && (buf[i + 1] & 0xe0) === 0xa0  // surrogate (U+D800 - U+DFFF)
       ) {
         return false;
-      } else {
-        i += 3;
       }
+
+      i += 3;
     } else if ((buf[i] & 0xf8) === 0xf0) {  // 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
       if (
         i + 3 >= len ||
@@ -48,15 +48,15 @@ const isValidUTF8 = (buf) => {
         buf[i] === 0xf4 && buf[i + 1] > 0x8f || buf[i] > 0xf4  // > U+10FFFF
       ) {
         return false;
-      } else {
-        i += 4;
       }
+
+      i += 4;
     } else {
       return false;
     }
   }
 
   return true;
-};
+}
 
 module.exports = isValidUTF8;
diff --git a/src/validation.c b/src/validation.c
index 4796d93..d5f1728 100644
--- a/src/validation.c
+++ b/src/validation.c
@@ -36,13 +36,13 @@ napi_value IsValidUTF8(napi_env env, napi_callback_info info) {
       uint64_t chunk;
       memcpy(&chunk, buf + i, 8);
 
-      if ((chunk & 0x8080808080808080) == 0) {
+      if ((chunk & 0x8080808080808080) == 0x00) {
         i = j;
         continue;
       }
     }
 
-    while ((buf[i] & 0x80) == 0) { // 0xxxxxxx
+    while ((buf[i] & 0x80) == 0x00) { // 0xxxxxxx
       if (++i == len) {
         goto exit;
       }