diff --git a/lib/index.js b/lib/index.js
index 8a0811c4..4faee7a6 100755
--- a/lib/index.js
+++ b/lib/index.js
@@ -59,8 +59,8 @@ function toIdentifierCase( text ) {
 				return word.toLowerCase();
 			}
 			return (
-				word.substr( 0, 1 ).toUpperCase()
-				+ word.substr( 1 ).toLowerCase()
+				word.slice( 0, 1 ).toUpperCase()
+				+ word.slice( 1 ).toLowerCase()
 			);
 		} )
 		.join( '' );