diff --git a/service_map.go b/service_map.go
index e68f0d5..1d34844 100644
--- a/service_map.go
+++ b/service_map.go
@@ -116,7 +116,7 @@ Loop:
 			if returnType := mtype.Out(1); returnType != typeOfError {
 				continue Loop
 			}
-			returnType = mtype.Out(1).Elem()
+			returnType = mtype.Out(0).Elem()
 		default:
 			continue
 		}