diff --git a/base/expr.jl b/base/expr.jl
index 5952904b3d17b..e007306063db1 100644
--- a/base/expr.jl
+++ b/base/expr.jl
@@ -1044,6 +1044,7 @@ end
     @atomic order ex
 
 Mark `var` or `ex` as being performed atomically, if `ex` is a supported expression.
+If no `order` is specified it defaults to :sequentially_consistent.
 
     @atomic a.b.x = new
     @atomic a.b.x += addend