diff --git a/csharp/src/Google.Protobuf/WritingPrimitives.cs b/csharp/src/Google.Protobuf/WritingPrimitives.cs
index 8d8dccc394ad..b6ed90cdf5f6 100644
--- a/csharp/src/Google.Protobuf/WritingPrimitives.cs
+++ b/csharp/src/Google.Protobuf/WritingPrimitives.cs
@@ -202,7 +202,8 @@ public static void WriteString(ref Span<byte> buffer, ref WriterInternalState st
                         ? WriteAsciiStringToBuffer(ref sourceChars, ref destinationBytes, value, length)
                         : 0;
 
-                    // This avoids bound checks
+                    // Process any remaining, 1 char at a time.
+                    // Avoid bounds checking with ref + Unsafe
                     for (; currentIndex < length; currentIndex++)
                     {
                         Unsafe.AddByteOffset(ref destinationBytes, (IntPtr)currentIndex) = (byte)Unsafe.AddByteOffset(ref sourceChars, (IntPtr)(currentIndex * 2));