diff --git a/django/contrib/admin/options.py b/django/contrib/admin/options.py
index 2099d14861..2913107b9c 100644
--- a/django/contrib/admin/options.py
+++ b/django/contrib/admin/options.py
@@ -858,15 +858,20 @@ class ModelAdmin(BaseModelAdmin):
     def _get_base_actions(self):
         """Return the list of actions, prior to any request-based filtering."""
         actions = []
+        base_actions = (self.get_action(action) for action in self.actions or [])
+        # get_action might have returned None, so filter any of those out.
+        base_actions = [action for action in base_actions if action]
+        base_action_names = {name for _, name, _ in base_actions}
 
         # Gather actions from the admin site first
         for (name, func) in self.admin_site.actions:
+            if name in base_action_names:
+                continue
             description = getattr(func, 'short_description', name.replace('_', ' '))
             actions.append((func, name, description))
         # Add actions from this ModelAdmin.
-        actions.extend(self.get_action(action) for action in self.actions or [])
-        # get_action might have returned None, so filter any of those out.
-        return filter(None, actions)
+        actions.extend(base_actions)
+        return actions
 
     def _filter_actions_by_permissions(self, request, actions):
         """Filter out any actions that the user doesn't have access to."""
diff --git a/tests/modeladmin/test_actions.py b/tests/modeladmin/test_actions.py
index a33c1811b2..76f2f96c03 100644
--- a/tests/modeladmin/test_actions.py
+++ b/tests/modeladmin/test_actions.py
@@ -76,3 +76,42 @@ class AdminActionsTests(TestCase):
         ma2 = AdminB(Band, admin.AdminSite())
         action_names = [name for _, name, _ in ma2._get_base_actions()]
         self.assertEqual(action_names, ['delete_selected'])
+
+    def test_actions_replace_global_action(self):
+        def global_action_1(modeladmin, request, queryset):
+            pass
+
+        def global_action_2(modeladmin, request, queryset):
+            pass
+
+        global_action_1.short_description = 'Site-wide admin action 1.'
+        global_action_2.short_description = 'Site-wide admin action 2.'
+        admin.site.add_action(global_action_1, name='custom_action_1')
+        admin.site.add_action(global_action_2, name='custom_action_2')
+
+        def custom_action_1(modeladmin, request, queryset):
+            pass
+
+        custom_action_1.short_description = 'Local admin action 1.'
+
+        class BandAdmin(admin.ModelAdmin):
+            actions = [custom_action_1, 'custom_action_2']
+
+            def custom_action_2(self, request, queryset):
+                pass
+
+            custom_action_2.short_description = 'Local admin action 2.'
+
+        ma = BandAdmin(Band, admin.site)
+        self.assertEqual(ma.check(), [])
+        self.assertEqual(
+            [
+                desc
+                for _, name, desc in ma._get_base_actions()
+                if name.startswith('custom_action')
+            ],
+            [
+                'Local admin action 1.',
+                'Local admin action 2.',
+            ],
+        )