diff --git a/src/signal_type.h b/src/signal_type.h
--- a/src/signal_type.h
+++ b/src/signal_type.h
@@ -12,6 +12,8 @@
 #ifndef SIGNAL_TYPE_H
 #define SIGNAL_TYPE_H
 
+#include "core/enum_type.hpp"
+
 /** Variant of the signal, i.e. how does the signal look? */
 enum SignalVariant {
 	SIG_ELECTRIC  = 0, ///< Light signal