diff --git a/distrho/extra/Runner.hpp b/distrho/extra/Runner.hpp
index cb6a494a..0f9dddbe 100644
--- a/distrho/extra/Runner.hpp
+++ b/distrho/extra/Runner.hpp
@@ -22,6 +22,7 @@
 #ifndef DISTRHO_OS_WASM
 # include "Thread.hpp"
 #else
+# include "String.hpp"
 # include <emscripten/emscripten.h>
 #endif