diff --git a/README.md b/README.md
index b84a68b..c7f8d06 100644
--- a/README.md
+++ b/README.md
@@ -179,10 +179,11 @@ A message has:
   the SimpleX relay, to the second; for a sent one, when the bot sent
   it.
 
-The answer is `400` if the query cannot be read (it holds a `;`, or a
-`%` not followed by two hexadecimal digits) or `count` is not a whole
-number from 1 to 100, and `404` if `GET /api/v1/chats` does not list
-`id`.
+The answer is `400` if `count` is not a whole number from 1 to 100, and
+`404` if `GET /api/v1/chats` does not list `id`. A query the server
+cannot read gets `400` with `the query cannot be read`; examples are a
+query that holds a `;`, a `%` not followed by two hexadecimal digits, or
+more than 10,000 parts separated by `&`.
 
 ### `POST /api/v1/chats/{id}/messages`
 
diff --git a/internal/api/messages_test.go b/internal/api/messages_test.go
index c56322b..24d1de7 100644
--- a/internal/api/messages_test.go
+++ b/internal/api/messages_test.go
@@ -152,6 +152,7 @@ func TestMessagesCount(t *testing.T) {
 
 // TestMessagesUnreadableQuery: a query that cannot be decoded is refused
 // with a sentence that says so, whether or not the bad part is count.
+// The last query has 10,001 parts, more than Go's url.ParseQuery takes.
 func TestMessagesUnreadableQuery(t *testing.T) {
 	t.Parallel()
 
@@ -159,6 +160,7 @@ func TestMessagesUnreadableQuery(t *testing.T) {
 
 	for _, query := range []string{
 		"?count=1%", "?count=5&x=%zz", "?x=%zz", "?count=5;x=1",
+		"?count=5" + strings.Repeat("&", 10000),
 	} {
 		client := &fakeClient{contacts: oneChat()}
 		rec := request(t, newAPI(credential, client),