diff --git a/reference/mongo/readpreferences.xml b/reference/mongo/readpreferences.xml
index 42cdcd4c97..32676c972d 100644
--- a/reference/mongo/readpreferences.xml
+++ b/reference/mongo/readpreferences.xml
@@ -186,12 +186,8 @@
    for tag sets.
   </para>
   <para>
-   When specifying read preference modes in a query string, the names
-   <literal>primary</literal>, <literal>primaryPreferred</literal>,
-   <literal>secondary</literal>, <literal>secondaryPreferred</literal>, and
-   <literal>nearest</literal> should be used instead of the constants for the
-   <literal>readPreference</literal> value. Tag sets for the
-   <literal>readPreferenceTags</literal> value should be a comma-delimited
+   When specifying read preference modes in a query string, the Tag sets for
+   the <literal>readPreferenceTags</literal> value should be a comma-delimited
    sequence of colon-delimited key/value pairs.
   </para>
   <note>
@@ -203,6 +199,14 @@
     they appear in the query string.
    </para>
   </note>
+  <warning>
+   <para>
+    If the driver cannot find a matching TagSet the read will fail!  It is
+    your responsibility of providing suitable fallback, such as an empty
+    <literal>readPreferenceTags</literal> value to fallback to "no TagSet
+    preference".
+   </para>
+  </warning>
   <para>
    <example>
     <title>Connection URI read preferences with query string syntax</title>