diff --git a/src/output/Wrapper.hxx b/src/output/Wrapper.hxx
index f2d212257..8c433f721 100644
--- a/src/output/Wrapper.hxx
+++ b/src/output/Wrapper.hxx
@@ -20,6 +20,7 @@
 #ifndef MPD_OUTPUT_WRAPPER_HXX
 #define MPD_OUTPUT_WRAPPER_HXX
 
+#include "Internal.hxx"
 #include "util/Cast.hxx"
 
 #include <chrono>