diff --git a/12-range_tree/cpp/range_tree.h b/12-range_tree/cpp/range_tree.h
index 61d238ce68fc5df8ac00910dbabe3971df423b4e..a5ca59475a82ca15e714bb4bbfd91c5aa20280e0 100644
--- a/12-range_tree/cpp/range_tree.h
+++ b/12-range_tree/cpp/range_tree.h
@@ -148,7 +148,7 @@ class Tree {
         }
     }
 
-    // Return number of elements in range [left, right].
+    // Return the sum of elements with keys in range [left, right].
     //
     // Given a closed range [left, right], return the sum of values of elements
     // in the range, i.e., sum(value | (key, value) in tree, left <= key <= right).
diff --git a/12-range_tree/python/range_tree.py b/12-range_tree/python/range_tree.py
index 161f79d6bd50636b6d03ac15426c8b763c2858d2..3288ca977f3849f96dc28e6c8e17f6fa9bad69b2 100644
--- a/12-range_tree/python/range_tree.py
+++ b/12-range_tree/python/range_tree.py
@@ -121,7 +121,7 @@ class Tree:
                 right.parent = self.root
 
     def range_sum(self, left, right):
-        """Return number of elements in range [left, right]
+        """Return the sum of elements with keys in range [left, right]
 
         Given a closed range [left, right], return the sum of values of elements
         in the range, i.e., sum(value | (key, value) in tree, left <= key <= right).