diff --git a/Sources/Identifier.swift b/Sources/Identifier.swift
index a1b5a8b..ac378b9 100644
--- a/Sources/Identifier.swift
+++ b/Sources/Identifier.swift
@@ -44,9 +44,9 @@ extension Identifier {
         }
         
         let numericCharacters: [String] = (0...9).map { "\($0)" }
-        let type = identifierString.characters.prefix(while: { !numericCharacters.contains(String($0))})
+        let type = identifierString.prefix(while: { !numericCharacters.contains(String($0))})
 
-        let version = identifierString.characters.suffix(from: type.endIndex)
+        let version = identifierString.suffix(from: type.endIndex)
             .split(separator: ",")
             .map { Int(String($0)) }