diff -u b/core/modules/workflows/src/Entity/Workflow.php b/core/modules/workflows/src/Entity/Workflow.php
--- b/core/modules/workflows/src/Entity/Workflow.php
+++ b/core/modules/workflows/src/Entity/Workflow.php
@@ -407,9 +407,9 @@
         throw new \InvalidArgumentException("The state '$from_state_id' does not exist in workflow '{$this->id()}'");
       }
       if ($this->hasTransitionFromStateToState($from_state_id, $this->transitions[$transition_id]['to'])) {
-        $transition = $this->getTransitionFromStateToState($from_state_id, $this->transitions[$transition_id]['to']);
-        if ($transition_id !== $transition->id()) {
-          throw new \InvalidArgumentException("The '{$transition->id()}' transition already allows '$from_state_id' to '{$this->transitions[$transition_id]['to']}' transitions in workflow '{$this->id()}'");
+        $existing_transition = $this->getTransitionFromStateToState($from_state_id, $this->transitions[$transition_id]['to']);
+        if ($transition_id !== $existing_transition->id()) {
+          throw new \InvalidArgumentException("The '{$existing_transition->id()}' transition already allows '$from_state_id' to '{$this->transitions[$transition_id]['to']}' transitions in workflow '{$this->id()}'");
         }
       }
     }
@@ -432,7 +432,7 @@
       throw new \InvalidArgumentException("The transition '$transition_id' does not exist in workflow '{$this->id()}'");
     }
 
-    // Ensure that the states exist.
+    // Ensure that the state the transition is to be changed to actually exists.
     if (!$this->hasState($to_state_id)) {
       throw new \InvalidArgumentException("The state '$to_state_id' does not exist in workflow '{$this->id()}'");
     }
@@ -448,7 +448,7 @@
       }
     }
 
-    // Update the transitions.
+    // Update the stored transitions with the new to state.
     $this->transitions[$transition_id]['to'] = $to_state_id;
 
     return $this;