diff --git a/doc/design/api.md b/doc/design/api.md
index d8825389cb694794eef0e479bc04c7e7c801a8ca..fe37cf091c5298f6fe034f5fb5977c155ca85ae9 100644
--- a/doc/design/api.md
+++ b/doc/design/api.md
@@ -12,7 +12,7 @@ Evaluator = {Model*, activations}
 - forward
 - test
 
-GradientMachine = {Model*, gradients}
+GradientMachine = {Evaluator*, gradients}
 - backward
 
 Optimizer = {Model*, Evaluator*, GradientMachine*}