diff --git a/doc/design/api.md b/doc/design/api.md
index fe37cf091c5298f6fe034f5fb5977c155ca85ae9..17ab50fdb26e6463a03dec87acabd49c070d3999 100644
--- a/doc/design/api.md
+++ b/doc/design/api.md
@@ -15,7 +15,7 @@ Evaluator = {Model*, activations}
 GradientMachine = {Evaluator*, gradients}
 - backward
 
-Optimizer = {Model*, Evaluator*, GradientMachine*}
+Optimizer = {Model*, GradientMachine*}
 - train
 - update
 - checkpoint