diff --git a/doc/src/sgml/trigger.sgml b/doc/src/sgml/trigger.sgml
index a5390ff644..31626536a2 100644
--- a/doc/src/sgml/trigger.sgml
+++ b/doc/src/sgml/trigger.sgml
@@ -354,6 +354,17 @@
     to avoid infinite recursion in such scenarios.
    </para>
 
+   <para>
+    If a foreign key constraint specifies referential actions (that
+    is, cascading updates or deletes), those actions are performed via
+    ordinary SQL update or delete commands on the referencing table.
+    In particular, any triggers that exist on the referencing table
+    will be fired for those changes.  If such a trigger modifies or
+    blocks the effect of one of these commands, the end result could
+    be to break referential integrity.  It is the trigger programmer's
+    responsibility to avoid that.
+   </para>
+
    <para>
     <indexterm>
      <primary>trigger</primary>