diff --git a/distrho/src/DistrhoUI.cpp b/distrho/src/DistrhoUI.cpp
index 20e084f7..2a0d1d37 100644
--- a/distrho/src/DistrhoUI.cpp
+++ b/distrho/src/DistrhoUI.cpp
@@ -17,6 +17,8 @@
 #include "src/DistrhoPluginChecks.h"
 #include "src/DistrhoDefines.h"
 
+#include <cstddef>
+
 #ifdef DISTRHO_PROPER_CPP11_SUPPORT
 # include <cstdint>
 #else