diff --git a/include/spdlog/details/fmt_helper.h b/include/spdlog/details/fmt_helper.h
index 81181c6c..bf9dc71f 100644
--- a/include/spdlog/details/fmt_helper.h
+++ b/include/spdlog/details/fmt_helper.h
@@ -73,12 +73,13 @@ inline void pad_uint(T n, unsigned int width, memory_buf_t &dest)
 template<typename T>
 inline void pad3(T n, memory_buf_t &dest)
 {
+    static_assert(std::is_unsigned<T>::value, "pad_uint must get unsigned T");
     if(n < 1000)
     {
-        dest.push_back(n / 100 + '0');
+        dest.push_back(static_cast<char>(n / 100 + '0'));
         n = n % 100;
-        dest.push_back((n / 10) + '0');
-        dest.push_back((n % 10) + '0');
+        dest.push_back(static_cast<char>((n / 10) + '0'));
+        dest.push_back(static_cast<char>((n % 10) + '0'));
     }
     else
     {
@@ -86,8 +87,6 @@ inline void pad3(T n, memory_buf_t &dest)
     }
 }
 
-
-
 template<typename T>
 inline void pad6(T n, memory_buf_t &dest)
 {