core/config/schema/core.data_types.schema.yml                     | 4 +++-
 core/modules/block/config/schema/block.schema.yml                 | 4 +++-
 core/modules/shortcut/config/schema/shortcut.schema.yml           | 4 +++-
 core/modules/system/config/schema/system.schema.yml               | 4 +++-
 .../KernelTests/Core/Config/ConfigEntityValidationTestBase.php    | 8 ++++++--
 5 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/core/config/schema/core.data_types.schema.yml b/core/config/schema/core.data_types.schema.yml
index a115ae89c3..c875fc2d6b 100644
--- a/core/config/schema/core.data_types.schema.yml
+++ b/core/config/schema/core.data_types.schema.yml
@@ -99,7 +99,9 @@ machine_name:
   type: string
   label: 'Machine name'
   constraints:
-    Regex: '/^[a-z0-9_]+$/'
+    Regex:
+      pattern: '/^[a-z0-9_]+$/'
+      message: "The %value machine name is not valid."
     Length:
       # @see \Drupal\Core\Config\Entity\ConfigEntityStorage::MAX_ID_LENGTH
       max: 166
diff --git a/core/modules/block/config/schema/block.schema.yml b/core/modules/block/config/schema/block.schema.yml
index 64dda31dbb..8989c1d79e 100644
--- a/core/modules/block/config/schema/block.schema.yml
+++ b/core/modules/block/config/schema/block.schema.yml
@@ -11,7 +11,9 @@ block.block.*:
       # @see https://www.drupal.org/project/drupal/issues/2685917
       # @see https://www.drupal.org/project/drupal/issues/2043527
       constraints:
-        Regex: '/^[a-z0-9_.]+$/'
+        Regex:
+          pattern: '/^[a-z0-9_.]+$/'
+          message: "The %value machine name is not valid."
     theme:
       type: string
       label: 'Theme'
diff --git a/core/modules/shortcut/config/schema/shortcut.schema.yml b/core/modules/shortcut/config/schema/shortcut.schema.yml
index 6fceb5741e..8f32203c65 100644
--- a/core/modules/shortcut/config/schema/shortcut.schema.yml
+++ b/core/modules/shortcut/config/schema/shortcut.schema.yml
@@ -11,7 +11,9 @@ shortcut.set.*:
       # dashes but not underscores.
       # @see \Drupal\shortcut\ShortcutSetForm::form()
       constraints:
-        Regex: '/^[a-z0-9-]+$/'
+        Regex:
+          pattern: '/^[a-z0-9-]+$/'
+          message: "The %value machine name is not valid."
         Length:
           max: 23
     label:
diff --git a/core/modules/system/config/schema/system.schema.yml b/core/modules/system/config/schema/system.schema.yml
index 7dcfd4db58..cb2eadde35 100644
--- a/core/modules/system/config/schema/system.schema.yml
+++ b/core/modules/system/config/schema/system.schema.yml
@@ -215,7 +215,9 @@ system.menu.*:
       # underscores.
       # @see \Drupal\menu_ui\MenuForm::form()
       constraints:
-        Regex: '/^[a-z0-9-]+$/'
+        Regex:
+          pattern: '/^[a-z0-9-]+$/'
+          message: "The %value machine name is not valid."
         Length:
           max: 32
     label:
diff --git a/core/tests/Drupal/KernelTests/Core/Config/ConfigEntityValidationTestBase.php b/core/tests/Drupal/KernelTests/Core/Config/ConfigEntityValidationTestBase.php
index 2aa8cedb87..436f63adcc 100644
--- a/core/tests/Drupal/KernelTests/Core/Config/ConfigEntityValidationTestBase.php
+++ b/core/tests/Drupal/KernelTests/Core/Config/ConfigEntityValidationTestBase.php
@@ -102,14 +102,18 @@ public function testInvalidMachineNameCharacters(string $machine_name, bool $is_
     $constraints = $this->getMachineNameConstraints();
 
     $this->assertNotEmpty($constraints['Regex']);
-    $this->assertIsString($constraints['Regex']);
+    $this->assertIsArray($constraints['Regex']);
+    $this->assertArrayHasKey('pattern', $constraints['Regex']);
+    $this->assertIsString($constraints['Regex']['pattern']);
+    $this->assertArrayHasKey('message', $constraints['Regex']);
+    $this->assertIsString($constraints['Regex']['message']);
 
     $id_key = $this->entity->getEntityType()->getKey('id');
     if ($is_expected_to_be_valid) {
       $expected_errors = [];
     }
     else {
-      $expected_errors = [$id_key => 'This value is not valid.'];
+      $expected_errors = [$id_key => sprintf('The <em class="placeholder">&quot;%s&quot;</em> machine name is not valid.', $machine_name)];
     }
 
     $this->entity->set(