diff --git a/include/nlohmann/detail/output/binary_writer.hpp b/include/nlohmann/detail/output/binary_writer.hpp
index a388e5d61..c059c2602 100644
--- a/include/nlohmann/detail/output/binary_writer.hpp
+++ b/include/nlohmann/detail/output/binary_writer.hpp
@@ -1060,6 +1060,8 @@ class binary_writer
         oa->write_characters(
             reinterpret_cast<const CharType*>(value.data()),
             value.size());
+        // the terminating null byte is written explicitly rather than taken
+        // from the buffer, so that string_t::data() need not be null-terminated
         oa->write_character(to_char_type(0x00));
     }
 
@@ -1151,6 +1153,9 @@ class binary_writer
 
         const std::size_t embedded_document_size = std::accumulate(std::begin(value), std::end(value), static_cast<std::size_t>(0), [&array_index](std::size_t result, const typename BasicJsonType::array_t::value_type & el)
         {
+            // the index is built as a std::string, while calc_bson_element_size
+            // takes a string_t; convert explicitly, as the two are only
+            // implicitly convertible for some string types
             const auto key = std::to_string(array_index++);
             return result + calc_bson_element_size(string_t(key.data(), key.size()), el);
         });
diff --git a/include/nlohmann/json.hpp b/include/nlohmann/json.hpp
index 81c309e63..00ad4f7b9 100644
--- a/include/nlohmann/json.hpp
+++ b/include/nlohmann/json.hpp
@@ -403,6 +403,18 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @}
 
+    // Two template parameter requirements that would otherwise be silently
+    // violated: neither produces a diagnostic of its own, and both corrupt
+    // values rather than failing.
+
+    static_assert(sizeof(typename BinaryType::value_type) == 1,
+                  "BinaryType::value_type must be exactly one byte wide, "
+                  "because the binary readers and writers reinterpret the container's storage as raw bytes");
+
+    static_assert(sizeof(NumberUnsignedType) >= sizeof(NumberIntegerType),
+                  "NumberUnsignedType must be at least as wide as NumberIntegerType, "
+                  "because it has to hold the absolute value of every NumberIntegerType value");
+
   private:
 
     /// helper for exception-safe object creation
diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
index 32825843e..4696a43a7 100644
--- a/single_include/nlohmann/json.hpp
+++ b/single_include/nlohmann/json.hpp
@@ -18109,6 +18109,8 @@ class binary_writer
         oa->write_characters(
             reinterpret_cast<const CharType*>(value.data()),
             value.size());
+        // the terminating null byte is written explicitly rather than taken
+        // from the buffer, so that string_t::data() need not be null-terminated
         oa->write_character(to_char_type(0x00));
     }
 
@@ -18200,6 +18202,9 @@ class binary_writer
 
         const std::size_t embedded_document_size = std::accumulate(std::begin(value), std::end(value), static_cast<std::size_t>(0), [&array_index](std::size_t result, const typename BasicJsonType::array_t::value_type & el)
         {
+            // the index is built as a std::string, while calc_bson_element_size
+            // takes a string_t; convert explicitly, as the two are only
+            // implicitly convertible for some string types
             const auto key = std::to_string(array_index++);
             return result + calc_bson_element_size(string_t(key.data(), key.size()), el);
         });
@@ -21886,6 +21891,18 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
 
     /// @}
 
+    // Two template parameter requirements that would otherwise be silently
+    // violated: neither produces a diagnostic of its own, and both corrupt
+    // values rather than failing.
+
+    static_assert(sizeof(typename BinaryType::value_type) == 1,
+                  "BinaryType::value_type must be exactly one byte wide, "
+                  "because the binary readers and writers reinterpret the container's storage as raw bytes");
+
+    static_assert(sizeof(NumberUnsignedType) >= sizeof(NumberIntegerType),
+                  "NumberUnsignedType must be at least as wide as NumberIntegerType, "
+                  "because it has to hold the absolute value of every NumberIntegerType value");
+
   private:
 
     /// helper for exception-safe object creation