core/modules/system/config/schema/system.schema.yml | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/core/modules/system/config/schema/system.schema.yml b/core/modules/system/config/schema/system.schema.yml
index e6a5260d2b..3d5bee0bcf 100644
--- a/core/modules/system/config/schema/system.schema.yml
+++ b/core/modules/system/config/schema/system.schema.yml
@@ -237,6 +237,12 @@ system.action.*:
     id:
       type: machine_name
       label: 'ID'
+      # Actions have atypical machine names: they allow periods for historical reasons.
+      # @see user_user_role_insert()
+      constraints:
+        Regex:
+          pattern: '/^[a-z0-9_\.]+$/'
+          message: "The %value machine name is not valid."
     label:
       type: label
       label: 'Label'