diff --git a/doc/effective_go.html b/doc/effective_go.html
index 731959e408..6d53eefbc3 100644
--- a/doc/effective_go.html
+++ b/doc/effective_go.html
@@ -1431,9 +1431,7 @@ func Append(slice, data []byte) []byte {
         slice = newSlice
     }
     slice = slice[0:l+len(data)]
-    for i, c := range data {
-        slice[l+i] = c
-    }
+    copy(slice[l:], data)
     return slice
 }
 </pre>