diff --git a/db/constraints.sql b/db/constraints.sql
index e5d2cb3d4d..434662fdff 100644
--- a/db/constraints.sql
+++ b/db/constraints.sql
@@ -193,7 +193,9 @@ alter table consent
 alter table consent
     add foreign key(consent_type_id)
     references consent_type(id)
-    on update cascade;
+    on update cascade
+    on delete restrict;
+      -- explicit delete restrict on this foreign key
 
 alter table consent_type
     add index consent_name(shortname);
diff --git a/html/ops/db_update.php b/html/ops/db_update.php
index 5e5bf7356c..8bf58e9189 100644
--- a/html/ops/db_update.php
+++ b/html/ops/db_update.php
@@ -1200,7 +1200,8 @@ function update_9_12_2018() {
     do_query("alter table consent
        add foreign key(consent_type_id)
        references consent_type(id)
-       on update cascade;
+       on update cascade
+       on delete restrict;
     ");
 
     do_query("insert into consent_type