diff --git a/include/nlohmann/detail/output/serializer.hpp b/include/nlohmann/detail/output/serializer.hpp
index dfbe54329a..9c2182c4a4 100644
--- a/include/nlohmann/detail/output/serializer.hpp
+++ b/include/nlohmann/detail/output/serializer.hpp
@@ -499,7 +499,7 @@ class serializer
                     {
                         case error_handler_t::strict:
                         {
-                            std::string sn(3, '\0');
+                            std::string sn(9, '\0');
                             // NOLINTNEXTLINE(cppcoreguidelines-pro-type-vararg,hicpp-vararg)
                             (std::snprintf)(&sn[0], sn.size(), "%.2X", byte);
                             JSON_THROW(type_error::create(316, "invalid UTF-8 byte at index " + std::to_string(i) + ": 0x" + sn, BasicJsonType()));
@@ -594,7 +594,7 @@ class serializer
             {
                 case error_handler_t::strict:
                 {
-                    std::string sn(3, '\0');
+                    std::string sn(9, '\0');
                     // NOLINTNEXTLINE(cppcoreguidelines-pro-type-vararg,hicpp-vararg)
                     (std::snprintf)(&sn[0], sn.size(), "%.2X", static_cast<std::uint8_t>(s.back()));
                     JSON_THROW(type_error::create(316, "incomplete UTF-8 string; last byte: 0x" + sn, BasicJsonType()));
diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
index 8130c6aa85..942b600e75 100644
--- a/single_include/nlohmann/json.hpp
+++ b/single_include/nlohmann/json.hpp
@@ -16484,7 +16484,7 @@ class serializer
                     {
                         case error_handler_t::strict:
                         {
-                            std::string sn(3, '\0');
+                            std::string sn(9, '\0');
                             // NOLINTNEXTLINE(cppcoreguidelines-pro-type-vararg,hicpp-vararg)
                             (std::snprintf)(&sn[0], sn.size(), "%.2X", byte);
                             JSON_THROW(type_error::create(316, "invalid UTF-8 byte at index " + std::to_string(i) + ": 0x" + sn, BasicJsonType()));
@@ -16579,7 +16579,7 @@ class serializer
             {
                 case error_handler_t::strict:
                 {
-                    std::string sn(3, '\0');
+                    std::string sn(9, '\0');
                     // NOLINTNEXTLINE(cppcoreguidelines-pro-type-vararg,hicpp-vararg)
                     (std::snprintf)(&sn[0], sn.size(), "%.2X", static_cast<std::uint8_t>(s.back()));
                     JSON_THROW(type_error::create(316, "incomplete UTF-8 string; last byte: 0x" + sn, BasicJsonType()));