diff --git a/include/nlohmann/detail/output/binary_writer.hpp b/include/nlohmann/detail/output/binary_writer.hpp
index 842640503..c682e72dc 100644
--- a/include/nlohmann/detail/output/binary_writer.hpp
+++ b/include/nlohmann/detail/output/binary_writer.hpp
@@ -9,6 +9,7 @@
 #include <limits> // numeric_limits
 #include <string> // string
 #include <utility> // move
+#include <vector> // vector
 
 #include <nlohmann/detail/input/binary_reader.hpp>
 #include <nlohmann/detail/macro_scope.hpp>
@@ -900,7 +901,7 @@ class binary_writer
                         return ubjson_prefix(v, use_bjdata) == first_prefix;
                     });
 
-                    if (same_prefix && !(use_bjdata && std::string("[{SHTFNZ").find(first_prefix) != std::string::npos))
+                    if (same_prefix && !(use_bjdata && std::string("[{SHTFNZ").find(static_cast<char>(first_prefix)) != std::string::npos))
                     {
                         prefix_required = false;
                         oa->write_character(to_char_type('$'));
diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
index 5b8d054c6..974653623 100644
--- a/single_include/nlohmann/json.hpp
+++ b/single_include/nlohmann/json.hpp
@@ -13765,6 +13765,7 @@ class json_ref
 #include <limits> // numeric_limits
 #include <string> // string
 #include <utility> // move
+#include <vector> // vector
 
 // #include <nlohmann/detail/input/binary_reader.hpp>
 
@@ -14799,7 +14800,7 @@ class binary_writer
                         return ubjson_prefix(v, use_bjdata) == first_prefix;
                     });
 
-                    if (same_prefix && !(use_bjdata && std::string("[{SHTFNZ").find(first_prefix) != std::string::npos))
+                    if (same_prefix && !(use_bjdata && std::string("[{SHTFNZ").find(static_cast<char>(first_prefix)) != std::string::npos))
                     {
                         prefix_required = false;
                         oa->write_character(to_char_type('$'));