diff --git a/installer/data/mysql/atomicupdate/bug_42489.pl b/installer/data/mysql/atomicupdate/bug_42489.pl
new file mode 100755
index 0000000000..b68a270142
--- /dev/null
+++ b/installer/data/mysql/atomicupdate/bug_42489.pl
@@ -0,0 +1,20 @@
+use Modern::Perl;
+use Koha::Installer::Output qw(say_success);
+
+return {
+    bug_number  => "42489",
+    description => "Add RealTimeHoldsQueueUnallocated system preference",
+    up          => sub {
+        my ($args) = @_;
+        my ( $dbh, $out ) = @$args{qw(dbh out)};
+
+        $dbh->do(
+            q{
+            INSERT IGNORE INTO systempreferences (variable, value)
+            VALUES ('RealTimeHoldsQueueUnallocated', '0')
+        }
+        );
+
+        say_success( $out, "Added new system preference 'RealTimeHoldsQueueUnallocated'" );
+    },
+};
diff --git a/installer/data/mysql/mandatory/sysprefs.sql b/installer/data/mysql/mandatory/sysprefs.sql
index dc6fe6553e..13b13d8a9e 100644
--- a/installer/data/mysql/mandatory/sysprefs.sql
+++ b/installer/data/mysql/mandatory/sysprefs.sql
@@ -692,6 +692,7 @@ INSERT INTO systempreferences ( `variable`, `value` ) VALUES
 ('QuoteOfTheDay',''),
 ('RandomizeHoldsQueueWeight','0'),
 ('RealTimeHoldsQueue', '0'),
+('RealTimeHoldsQueueUnallocated', '0'),
 ('RecallsLog','1'),
 ('RecallsMaxPickUpDelay','7'),
 ('RecordLocalUseOnReturn','0'),
diff --git a/koha-tmpl/intranet-tmpl/prog/en/modules/admin/preferences/circulation.pref b/koha-tmpl/intranet-tmpl/prog/en/modules/admin/preferences/circulation.pref
index 5ef1d9316b..71721ab086 100644
--- a/koha-tmpl/intranet-tmpl/prog/en/modules/admin/preferences/circulation.pref
+++ b/koha-tmpl/intranet-tmpl/prog/en/modules/admin/preferences/circulation.pref
@@ -838,6 +838,13 @@ Circulation:
                   1: Enable
                   0: Disable
             - updating the holds queue in real time.
+        -
+            - "When RealTimeHoldsQueue is enabled:"
+            - pref: RealTimeHoldsQueueUnallocated
+              choices:
+                  1: only process unallocated holds
+                  0: rebuild the entire queue for the affected biblio
+            - ". Processing only unallocated holds is faster but will not recalculate existing allocations."
         -
             - pref: AllowHoldItemTypeSelection
               choices: