diff --git a/Sources/CryptoSwiftHMACModule.swift b/Sources/CryptoSwiftHMACModule.swift
index 47a2cfbb..a7293640 100644
--- a/Sources/CryptoSwiftHMACModule.swift
+++ b/Sources/CryptoSwiftHMACModule.swift
@@ -229,7 +229,7 @@ internal extension CSArrayType where Iterator.Element == UInt8 {
     internal func toHexString() -> String {
         return self.lazy.reduce("") {
             var s = String($1, radix: 16)
-            if s.characters.count == 1 {
+            if s.count == 1 {
                 s = "0" + s
             }
             return $0 + s