diff --git a/dba/davical.sql b/dba/davical.sql
index 7a6a51f7..501f46d0 100644
--- a/dba/davical.sql
+++ b/dba/davical.sql
@@ -394,7 +394,8 @@ CREATE TABLE calendar_attendee (
   attendee TEXT,
   role TEXT,
   rsvp BOOLEAN,
-  property TEXT -- The full text of the property
+  property TEXT, -- The full text of the property
+  PRIMARY KEY ( dav_id, attendee )
 );
 
 SELECT new_db_revision(1,2,8, 'Août' );
diff --git a/dba/patches/1.2.8.sql b/dba/patches/1.2.8.sql
index 6f816a2d..d10c3a10 100644
--- a/dba/patches/1.2.8.sql
+++ b/dba/patches/1.2.8.sql
@@ -99,7 +99,8 @@ CREATE TABLE calendar_attendee (
   attendee TEXT,
   role TEXT,
   rsvp BOOLEAN,
-  property TEXT -- The full text of the property
+  property TEXT, -- The full text of the property
+  PRIMARY KEY ( dav_id, attendee )
 );
 
 SELECT new_db_revision(1,2,8, 'Août' );