diff --git a/README.md b/README.md
index 230b1ed..9501e61 100644
--- a/README.md
+++ b/README.md
@@ -622,7 +622,7 @@ def add(x, y):
 ```
 
 ### LRU Cache
-**Decorator that caches function's return values.**
+**Decorator that caches function's return values. All arguments must be hashable.**
 ```python
 @lru_cache(maxsize=None)
 def fib(n):