diff --git a/src/serial_io.h b/src/serial_io.h
index d46e9687546d93af9c99339cdbe1d7dd72c87116..07df76fe869fa0612bba5cf953faadd8bc63f29e 100644
--- a/src/serial_io.h
+++ b/src/serial_io.h
@@ -31,6 +31,7 @@
 
 /* Includes. */
 #include "engine.h"
+#include "io_properties.h"
 #include "part.h"
 #include "units.h"