diff --git a/Tests/CBORTests/Extensions/Data+hexString.swift b/Tests/CBORTests/Extensions/Data+hexString.swift
index af21869..4ec6d23 100644
--- a/Tests/CBORTests/Extensions/Data+hexString.swift
+++ b/Tests/CBORTests/Extensions/Data+hexString.swift
@@ -12,7 +12,14 @@ import Foundation
 #endif
 
 extension Data {
+    private static let hexAlphabet = Array("0123456789abcdef".unicodeScalars)
+
     func hexString() -> String {
-        map { String(format: "%02hhX", $0) }.joined()
+        // I'd rather use: map { String(format: "%02hhX", $0) }.joined()
+        // but that doesn't compile on linux...
+        String(reduce(into: "".unicodeScalars) { result, value in
+            result.append(Self.hexAlphabet[Int(value / 0x10)])
+            result.append(Self.hexAlphabet[Int(value % 0x10)])
+        })
     }
 }