diff --git a/C4/Calendar.pm b/C4/Calendar.pm
index 3e92b0130b..8b067bd080 100644
--- a/C4/Calendar.pm
+++ b/C4/Calendar.pm
@@ -104,7 +104,7 @@ sub _init {
     $exceptions_sth->execute($branch);
     my %exception_holidays;
     while ( my $row = $exceptions_sth->fetchrow_hashref ) {
-        my ( $year, $month, $day ) = split( /-/, $row->{date} );
+        my ( $year, $month, $day ) = map { $_ + 0 } split( /-/, $row->{date} );
         $exception_holidays{"$year/$month/$day"}{title}       = $row->{title};
         $exception_holidays{"$year/$month/$day"}{description} = $row->{description};
         $exception_holidays{"$year/$month/$day"}{date}        = $row->{date};
@@ -115,7 +115,7 @@ sub _init {
     $single_sth->execute($branch);
     my %single_holidays;
     while ( my $row = $single_sth->fetchrow_hashref ) {
-        my ( $year, $month, $day ) = split( /-/, $row->{date} );
+        my ( $year, $month, $day ) = map { $_ + 0 } split( /-/, $row->{date} );
         $single_holidays{"$year/$month/$day"}{title}       = $row->{title};
         $single_holidays{"$year/$month/$day"}{description} = $row->{description};
         $single_holidays{"$year/$month/$day"}{date}        = $row->{date};
@@ -274,11 +274,18 @@ sub insert_single_holiday {
     unless ($date) {
         $date = sprintf( ISO_DATE_FORMAT, $options{year}, $options{month}, $options{day} );
     }
+    @options{qw(year month day)} = map { $_ + 0 } ( $date =~ m/(\d+)-(\d+)-(\d+)/ )
+        unless $options{day};
+
     Koha::Library::Calendar->new( branchcode => $self->{branchcode} )->add_single_closure(
         {
             date => $date, title => $options{title}, description => $options{description},
         }
     );
+
+    $self->{'single_holidays'}->{"$options{year}/$options{month}/$options{day}"}{title}       = $options{title};
+    $self->{'single_holidays'}->{"$options{year}/$options{month}/$options{day}"}{description} = $options{description};
+
     return $self;
 }
 
@@ -311,11 +318,19 @@ sub insert_exception_holiday {
     unless ($date) {
         $date = sprintf( ISO_DATE_FORMAT, $options{year}, $options{month}, $options{day} );
     }
+    @options{qw(year month day)} = map { $_ + 0 } ( $date =~ m/(\d+)-(\d+)-(\d+)/ )
+        unless $options{day};
+
     Koha::Library::Calendar->new( branchcode => $self->{branchcode} )->add_exception(
         {
             date => $date, title => $options{title}, description => $options{description},
         }
     );
+
+    $self->{'exception_holidays'}->{"$options{year}/$options{month}/$options{day}"}{title} = $options{title};
+    $self->{'exception_holidays'}->{"$options{year}/$options{month}/$options{day}"}{description} =
+        $options{description};
+
     return $self;
 }
 
diff --git a/t/db_dependent/Holidays.t b/t/db_dependent/Holidays.t
index 28fcd3a362..4572a668dc 100755
--- a/t/db_dependent/Holidays.t
+++ b/t/db_dependent/Holidays.t
@@ -18,7 +18,7 @@
 use Modern::Perl;
 
 use Test::NoWarnings;
-use Test::More tests => 15;
+use Test::More tests => 16;
 use Test::Exception;
 
 use DateTime;
@@ -386,5 +386,58 @@ subtest 'with a library that is *almost* never open' => sub {
     $schema->storage->txn_rollback;
 };
 
+subtest 'insert_single_holiday/insert_exception_holiday update the in-memory cache' => sub {
+    plan tests => 4;
+
+    $schema->storage->txn_begin;
+
+    my $branchcode = $builder->build( { source => 'Branch' } )->{branchcode};
+    my $calendar   = C4::Calendar->new( branchcode => $branchcode );
+
+    my $single_day = dt_from_string()->add( days => 10 );
+    $calendar->insert_single_holiday(
+        day         => $single_day->day,
+        month       => $single_day->month,
+        year        => $single_day->year,
+        title       => 'Single',
+        description => '',
+    );
+    is(
+        $calendar->isHoliday( $single_day->day, $single_day->month, $single_day->year ), 1,
+        'isHoliday sees a single holiday just inserted on the same C4::Calendar object'
+    );
+
+    # Close every weekday so exception_day is a holiday until the exception is added.
+    foreach my $weekday ( 0 .. 6 ) {
+        $calendar->insert_week_day_holiday( weekday => $weekday, title => '', description => '' );
+    }
+
+    # insert_exception_holiday called with 'date' rather than day/month/year,
+    # exercising the date-string derivation path.
+    my $exception_day = dt_from_string()->add( days => 20 );
+    $calendar->insert_exception_holiday(
+        date        => $exception_day->ymd,
+        title       => 'Exception',
+        description => '',
+    );
+    is(
+        $calendar->isHoliday( $exception_day->day, $exception_day->month, $exception_day->year ), 0,
+        'isHoliday sees an exception holiday just inserted on the same C4::Calendar object, overriding the weekday closure'
+    );
+
+    # A second, freshly instantiated C4::Calendar object should agree.
+    my $reloaded = C4::Calendar->new( branchcode => $branchcode );
+    is(
+        $reloaded->isHoliday( $single_day->day, $single_day->month, $single_day->year ), 1,
+        'A freshly instantiated C4::Calendar also sees the single holiday'
+    );
+    is(
+        $reloaded->isHoliday( $exception_day->day, $exception_day->month, $exception_day->year ), 0,
+        'A freshly instantiated C4::Calendar also sees the exception holiday'
+    );
+
+    $schema->storage->txn_rollback;
+};
+
 # Clear cache
 Koha::Caches->get_instance->flush_all;