diff --git a/include/nlohmann/detail/input/lexer.hpp b/include/nlohmann/detail/input/lexer.hpp
index 1b49d69b07..ab84828acf 100644
--- a/include/nlohmann/detail/input/lexer.hpp
+++ b/include/nlohmann/detail/input/lexer.hpp
@@ -1492,7 +1492,7 @@ class lexer
     position_t position {};
 
     /// raw input token string (for error messages)
-    std::vector<char> token_string {};
+    std::vector<signed char> token_string {};
 
     /// buffer for variable-length tokens (numbers, strings)
     string_t token_buffer {};
diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
index 77bd1739c8..e050e9c9e4 100644
--- a/single_include/nlohmann/json.hpp
+++ b/single_include/nlohmann/json.hpp
@@ -8622,7 +8622,7 @@ class lexer
     position_t position {};
 
     /// raw input token string (for error messages)
-    std::vector<char> token_string {};
+    std::vector<signed char> token_string {};
 
     /// buffer for variable-length tokens (numbers, strings)
     string_t token_buffer {};