diff --git a/src/mynonlinearity.cc b/src/mynonlinearity.cc
index 4b95a4f5d7b5673afa909da6dbdc857b7b8825af..b29e8bcaae9ef6e82699ab6218c48b1c7191858e 100644
--- a/src/mynonlinearity.cc
+++ b/src/mynonlinearity.cc
@@ -49,5 +49,6 @@ class MyNonlinearity {
     dom[1] = std::numeric_limits<double>::max();
   }
 
+private:
   OuterFunction func_;
 };