diff --git a/core/modules/book/src/BookManager.php b/core/modules/book/src/BookManager.php
index eb5b582..478ff86 100644
--- a/core/modules/book/src/BookManager.php
+++ b/core/modules/book/src/BookManager.php
@@ -252,7 +252,7 @@ public function updateOutline(NodeInterface $node) {
     // Prevent changes to the book outline if the node being saved is not the
     // default revision.
     if (!$node->isDefaultRevision()) {
-      drupal_set_message($this->t('You can only change the book outline for the published version of this content.'), 'error');
+      drupal_set_message($this->t('This is not the default revision. You can only change the book outline for the <em>published</em> version of this content.'), 'error');
       return FALSE;
     }
 
diff --git a/core/modules/book/tests/src/Functional/BookContentModerationTest.php b/core/modules/book/tests/src/Functional/BookContentModerationTest.php
index 0b9c831..3a372a9 100644
--- a/core/modules/book/tests/src/Functional/BookContentModerationTest.php
+++ b/core/modules/book/tests/src/Functional/BookContentModerationTest.php
@@ -60,7 +60,7 @@ public function testBookWithForwardRevisions() {
     $edit['book[pid]'] = $book_1_nodes[3]->id();
     $this->drupalPostForm('node/' . $book_1_nodes[1]->id() . '/edit', $edit, t('Save and Create New Draft'));
 
-    $this->assertSession()->pageTextContains('You can only change the book outline for the published version of this content.');
+    $this->assertSession()->pageTextContains('This is not the default revision. You can only change the book outline for the published version of this content.');
 
     // Check that the book outline did not change.
     $this->book = $book_1;
@@ -71,7 +71,7 @@ public function testBookWithForwardRevisions() {
     $edit['book[bid]'] = $book_2->id();
     $this->drupalPostForm('node/' . $book_1_nodes[1]->id() . '/edit', $edit, t('Save and Create New Draft'));
 
-    $this->assertSession()->pageTextContains('You can only change the book outline for the published version of this content.');
+    $this->assertSession()->pageTextContains('This is not the default revision. You can only change the book outline for the published version of this content.');
 
     // Check that the book outline did not change.
     $this->book = $book_1;