diff --git a/src/google/protobuf/descriptor.proto b/src/google/protobuf/descriptor.proto
index 8f619e85cd..6805b9b4b6 100644
--- a/src/google/protobuf/descriptor.proto
+++ b/src/google/protobuf/descriptor.proto
@@ -448,12 +448,16 @@ message FileOptions {
   // This option does nothing.
   optional bool java_generate_equals_and_hash = 20 [deprecated=true];
 
-  // If set true, then the Java2 code generator will generate code that
-  // throws an exception whenever an attempt is made to assign a non-UTF-8
-  // byte sequence to a string field.
-  // Message reflection will do the same.
-  // However, an extension field still accepts non-UTF-8 byte sequences.
-  // This option has no effect on when used with the lite runtime.
+  // A proto2 file can set this to true to opt in to UTF-8 checking for Java,
+  // which will throw an exception if invalid UTF-8 is parsed from the wire or
+  // assigned to a string field.
+  //
+  // TODO: clarify exactly what kinds of field types this option
+  // applies to, and update these docs accordingly.
+  //
+  // Proto3 files already perform these checks. Setting the option explicitly to
+  // false has no effect: it cannot be used to opt proto3 files out of UTF-8
+  // checks.
   optional bool java_string_check_utf8 = 27 [default = false];
 
   // Generated classes can be optimized for speed or code size.