Only modify the keys if there are duplicates

src/Illuminate/Cache/RateLimiter.php

@@ -76,8 +76,16 @@ public function limiter($name)
                 return $result;
             }
 
+            $duplicates = collect($result)->duplicates('key');
+
+            if ($duplicates->isEmpty()) {
+                return $result;
+            }
+
             foreach ($result as $limit) {
-                $limit->key = $limit->uniqueKey();
+                if ($duplicates->contains($limit->key)) {
+                    $limit->key = $limit->fallbackKey();
+                }
             }
 
             return $result;

src/Illuminate/Cache/RateLimiting/Limit.php

@@ -144,16 +144,12 @@ public function response(callable $callback)
     }
 
     /**
-     * Retrieve a unique key for the limit.
+     * Retrieve a fallback key for the limit.
      *
      * @return string
      */
-    public function uniqueKey()
+    public function fallbackKey()
     {
-        if ($this->key !== '') {
-            return $this->key;
-        }
-
         return "attempts:{$this->maxAttempts}:decay:{$this->decaySeconds}";
     }
 }