diff --git a/src/message/native_types.cpp b/src/message/native_types.cpp
index f0a7747..08ccd02 100644
--- a/src/message/native_types.cpp
+++ b/src/message/native_types.cpp
@@ -3,6 +3,7 @@
 #include <algorithm>
 #include <array>
 #include <cctype>
+#include <cstdint>
 
 namespace sdbusplus
 {
@@ -14,8 +15,8 @@
 constexpr std::array<char, 16> hex{'0', '1', '2', '3', '4', '5', '6', '7',
                                    '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'};
 
-constexpr std::array<char, 256> unhex = [] {
-    std::array<char, 256> ret{};
+constexpr std::array<int8_t, 256> unhex = [] {
+    std::array<int8_t, 256> ret{};
     for (size_t i = 0; i < ret.size(); ++i)
     {
         ret[i] = -1;