diff --git a/base/essentials.jl b/base/essentials.jl
index bbba482b84974..ec113c39fa764 100644
--- a/base/essentials.jl
+++ b/base/essentials.jl
@@ -540,7 +540,7 @@ element `i` of array `A` is skipped to improve performance.
 ```julia
 function sum(A::AbstractArray)
     r = zero(eltype(A))
-    for i = 1:length(A)
+    for i in eachindex(A)
         @inbounds r += A[i]
     end
     return r