diff --git a/t/db_dependent/Koha/Plugins/Barcode_transform_hooks.t b/t/db_dependent/Koha/Plugins/Barcode_transform_hooks.t
index cbd50360df..7b4095beb8 100755
--- a/t/db_dependent/Koha/Plugins/Barcode_transform_hooks.t
+++ b/t/db_dependent/Koha/Plugins/Barcode_transform_hooks.t
@@ -47,15 +47,17 @@ subtest 'patron_barcode_transform() and item_barcode_transform() hook tests' =>
 
     $schema->storage->txn_begin;
 
-    # Avoid testing useless warnings
-    my $test_plugin = Test::MockModule->new('Koha::Plugin::Test');
-    $test_plugin->mock( 'after_item_action',   undef );
-    $test_plugin->mock( 'after_biblio_action', undef );
-
     my $plugins = Koha::Plugins->new;
 
     warning_is { $plugins->InstallPlugins; } undef;
 
+    # Avoid testing useless warnings. Must be applied after InstallPlugins,
+    # which reloads plugin classes from disk and would otherwise wipe the
+    # mocks.
+    my $test_plugin = Test::MockModule->new('Koha::Plugin::Test');
+    $test_plugin->mock( 'after_item_action',   undef );
+    $test_plugin->mock( 'after_biblio_action', undef );
+
     C4::Context->dbh->do("DELETE FROM plugin_methods WHERE plugin_class LIKE '%TestBarcodes%'");
 
     my $plugin = Koha::Plugin::Test->new->enable;
diff --git a/t/db_dependent/Koha/Plugins/Plugins.t b/t/db_dependent/Koha/Plugins/Plugins.t
index 97b0fcbee9..c2996520eb 100755
--- a/t/db_dependent/Koha/Plugins/Plugins.t
+++ b/t/db_dependent/Koha/Plugins/Plugins.t
@@ -26,7 +26,7 @@ use List::MoreUtils           qw(none);
 use Module::Load::Conditional qw(can_load);
 use Test::MockModule;
 use Test::NoWarnings;
-use Test::More tests => 21;
+use Test::More tests => 22;
 use Test::Warn;
 use Test::Exception;
 
@@ -264,6 +264,72 @@ subtest 'InstallPlugins() tests' => sub {
     $schema->storage->txn_rollback;
 };
 
+subtest 'InstallPlugins() reloads stale symbol tables tests' => sub {
+
+    plan tests => 5;
+
+    $schema->storage->txn_begin;
+
+    Koha::Plugins::Methods->delete;
+    $schema->resultset('PluginData')->delete;
+
+    my $plugins = Koha::Plugins->new( { enable_plugins => 1 } );
+    $plugins->InstallPlugins( { include => ['Koha::Plugin::Test'] } );
+
+    # Simulate the stale-symbol-table scenario that a long-lived Plack worker
+    # would hit when a plugin is upgraded in place: inject a method into the
+    # loaded package that is not present in the .pm file on disk, and add a
+    # matching plugin_methods row as if a previous version of the plugin had
+    # this method and had loaded the older version into memory.
+    # A run of InstallPlugins should reload from disk and the phantom method
+    # should disappear.
+    {
+        no strict 'refs';
+        *{'Koha::Plugin::Test::stale_phantom_method'} = sub { 1 };
+    }
+
+    Koha::Plugins::Method->new(
+        {
+            plugin_class  => 'Koha::Plugin::Test',
+            plugin_method => 'stale_phantom_method',
+        }
+    )->store;
+
+    ok(
+        Koha::Plugin::Test->can('stale_phantom_method'),
+        'Phantom method is in the in-memory symbol table before reinstall'
+    );
+
+    ok(
+        Koha::Plugins::Methods->search(
+            { plugin_class => 'Koha::Plugin::Test', plugin_method => 'stale_phantom_method' }
+        )->count,
+        'Phantom method row is present in plugin_methods before reinstall'
+    );
+
+    $plugins->InstallPlugins( { include => ['Koha::Plugin::Test'] } );
+
+    ok(
+        !Koha::Plugin::Test->can('stale_phantom_method'),
+        'Phantom method is gone from the symbol table after reinstall (package was reloaded)'
+    );
+
+    is(
+        Koha::Plugins::Methods->search(
+            { plugin_class => 'Koha::Plugin::Test', plugin_method => 'stale_phantom_method' }
+        )->count,
+        0,
+        'Phantom method absent from the .pm file is not persisted to plugin_methods after reinstall'
+    );
+
+    ok(
+        Koha::Plugins::Methods->search( { plugin_class => 'Koha::Plugin::Test', plugin_method => 'tool' } )->count,
+        'Real methods from the .pm file are persisted to plugin_methods'
+    );
+
+    $schema->storage->txn_rollback;
+};
+
 subtest 'Version upgrade tests' => sub {
 
     plan tests => 1;