diff --git a/src/doc/guide-lifetimes.md b/src/doc/guide-lifetimes.md
index 545d286c5d7..dd79d63d514 100644
--- a/src/doc/guide-lifetimes.md
+++ b/src/doc/guide-lifetimes.md
@@ -307,7 +307,7 @@ copying.
 # }
 fn compute_area(shape: &Shape) -> f64 {
     match *shape {
-        Circle(_, radius) => 2.0 * std::f64::consts::PI * radius * radius,
+        Circle(_, radius) => std::f64::consts::PI * radius * radius,
         Rectangle(_, ref size) => size.w * size.h
     }
 }