diff --git a/src/components/PresentsPuzzle.tsx b/src/components/PresentsPuzzle.tsx
index b465e21..e8f183a 100644
--- a/src/components/PresentsPuzzle.tsx
+++ b/src/components/PresentsPuzzle.tsx
@@ -273,6 +273,9 @@ const PresentsPuzzle = ({
   };
 
   const stepToEnd = () => {
+    // Don't do anything if already at end or winner already determined
+    if (currentStep >= 99 || winner !== null) return;
+    
     const { presents, aliceOrder: aOrder, bobOrder: bOrder } = initializeSimulation();
     
     let aliceCount = 0;
@@ -465,7 +468,7 @@ const PresentsPuzzle = ({
             </Button>
             <Button 
               onClick={stepToEnd} 
-              disabled={isRunning || currentStep >= 99} 
+              disabled={isRunning || currentStep >= 99 || winner !== null} 
               variant="outline"
               className="gap-2"
               title="Step to end"