diff --git a/README.md b/README.md
index a77dffd..5c9596b 100644
--- a/README.md
+++ b/README.md
@@ -581,7 +581,7 @@ for i in range(10):
 ```
 
 ### Map, Filter, Reduce
-```python
+```python3
 from functools import reduce
 <iter> = map(lambda x: x + 1, range(10))            # (1, 2, ..., 10)
 <iter> = filter(lambda x: x > 5, range(10))         # (6, 7, 8, 9)