diff --git a/README.md b/README.md
index 230fa5b..9e202e9 100644
--- a/README.md
+++ b/README.md
@@ -14,7 +14,7 @@ but avoids the performance penalty of going through
 See also [`dtoa`](https://github.com/dtolnay/dtoa) for printing floating point
 primitives.
 
-## Performance
+## Performance (lower is better)
 
 ![performance](https://raw.githubusercontent.com/dtolnay/itoa/master/performance.png)