diff -u b/core/modules/workflows/tests/src/Functional/WorkflowUiTest.php b/core/modules/workflows/tests/src/Functional/WorkflowUiTest.php
--- b/core/modules/workflows/tests/src/Functional/WorkflowUiTest.php
+++ b/core/modules/workflows/tests/src/Functional/WorkflowUiTest.php
@@ -174,10 +174,24 @@
     $workflow = $workflow_storage->loadUnchanged('test');
     $this->assertTrue($workflow->getState('toteststate')->canTransitionTo('published'), 'Can transition from toteststate to published');
     $this->assertFalse($workflow->getState('toteststate')->canTransitionTo('draft'), 'Can no longer transition from toteststate to draft');
-    // Delete transition use in test changing the transition 'to' value.
+    // Create another new transition to help test that we cannot create a
+    // duplicate by changing the 'to' value.
+    $this->drupalGet('admin/config/workflow/workflows/manage/test');
+    $this->clickLink('Add a new transition');
+    $this->submitForm(['id' => 'totesttransitionduplicate', 'label' => 'ToTestTransitionDuplicate', 'from[toteststate]' => 'toteststate', 'to' => 'draft'], 'Save');
+    $this->assertSession()->pageTextContains('Created ToTestTransitionDuplicate transition.');
+    // Ensure that we cannot create a duplicate by changing the 'to' value.
+    $this->drupalGet('admin/config/workflow/workflows/manage/test/transition/totesttransitionduplicate');
+    $this->assertSession()->pageTextContains('ToTestTransitionDuplicate');
+    $this->submitForm(['from[toteststate]' => 'toteststate', 'to' => 'published'], 'Save');
+    $this->assertSession()->pageTextContains('The transition from ToTestState to Live already exists.');
+    // Delete transitions used in test changing the transition 'to' value.
     $this->drupalGet('admin/config/workflow/workflows/manage/test/transition/totesttransition');
     $this->clickLink('Delete');
     $this->submitForm([], 'Delete');
+    $this->drupalGet('admin/config/workflow/workflows/manage/test/transition/totesttransitionduplicate');
+    $this->clickLink('Delete');
+    $this->submitForm([], 'Delete');
     // Delete state use in test changing the transition 'to' value.
     $this->drupalGet('admin/config/workflow/workflows/manage/test/state/toteststate');
     $this->clickLink('Delete');