diff --git a/notimpl/readonly.cpp b/notimpl/readonly.cpp
index 1ae2b30..94d1702 100644
--- a/notimpl/readonly.cpp
+++ b/notimpl/readonly.cpp
@@ -18,6 +18,9 @@
 
 #include <stdexcept>
 
+namespace pid_control
+{
+
 void ReadOnly::write(double value)
 {
     throw std::runtime_error("Not supported.");
@@ -27,3 +30,5 @@
 {
     return;
 }
+
+} // namespace pid_control