diff --git a/gtk2_ardour/processor_box.cc b/gtk2_ardour/processor_box.cc
index c9b7e04a7c..aa8f285a43 100644
--- a/gtk2_ardour/processor_box.cc
+++ b/gtk2_ardour/processor_box.cc
@@ -21,6 +21,10 @@
 #include "gtk2ardour-config.h"
 #endif
 
+#ifdef COMPILER_MSVC
+#define rintf(x) round((x) + 0.5)
+#endif
+
 #include <cmath>
 #include <iostream>
 #include <set>