diff --git a/why-not-json.md b/why-not-json.md
index 9fc1f86..d8706bf 100644
--- a/why-not-json.md
+++ b/why-not-json.md
@@ -97,6 +97,13 @@ Some examples:
  - which, if any, of `{"a":1, "a":2}`, `{"a":1}` and `{"a":2}` are the
    same? Are all three legal?
  - are `{"päron":1}` and `{"päron":1}` the same or different?
+ - is `"\uD834"` a legal string? Is `"\uDD1E"`?[^unpaired-surrogates]
+
+[^unpaired-surrogates]:
+    [Section 8.2 of RFC 8259](https://tools.ietf.org/html/rfc8259#section-8.2)
+    discusses *unpaired UTF-16 surrogate* code points such as these, and
+    remarks that implementations differ in their treatment of them. Some
+    reject unpaired surrogates, some discard them, and some retain them.
 
 ## JSON can multiply nicely, but it can't add very well