diff --git a/src/stringify.js b/src/stringify.js
index d74b8e1d..3e66728d 100644
--- a/src/stringify.js
+++ b/src/stringify.js
@@ -7,7 +7,7 @@ import validate from './validate.js';
 const byteToHex = [];
 
 for (let i = 0; i < 256; ++i) {
-  byteToHex.push((i + 0x100).toString(16).substr(1));
+  byteToHex.push((i + 0x100).toString(16).slice(1));
 }
 
 export function unsafeStringify(arr, offset = 0) {
diff --git a/src/version.js b/src/version.js
index 2b993703..08ce2caa 100644
--- a/src/version.js
+++ b/src/version.js
@@ -5,7 +5,7 @@ function version(uuid) {
     throw TypeError('Invalid UUID');
   }
 
-  return parseInt(uuid.substr(14, 1), 16);
+  return parseInt(uuid.slice(14, 15), 16);
 }
 
 export default version;