diff --git a/include/villas/signal.h b/include/villas/signal.h
index 09487bda7..590f5932a 100644
--- a/include/villas/signal.h
+++ b/include/villas/signal.h
@@ -33,16 +33,22 @@ extern "C" {
 struct list;
 struct node;
 
+enum signal_format {
+	SIGNAL_FORMAT_FLOAT	= 0,
+	SIGNAL_FORMAT_INT	= 1,
+	SIGNAL_FORMAT_BOOL 	= 2,
+	SIGNAL_FORMAT_UNKNOWN	= -1
+};
+
 struct signal {
 	char *name;	/**< The name of the signal. */
 	char *unit;
 	int enabled;
-	enum {
-		SIGNAL_FORMAT_INTEGER,
-		SIGNAL_FORMAT_REAL
-	} format;
+	enum signal_format format;
 };
 
+int signal_init(struct signal *s);
+
 int signal_destroy(struct signal *s);
 
 int signal_parse(struct signal *s, json_t *cfg);
diff --git a/lib/signal.c b/lib/signal.c
index cf3dbcf1e..52829be11 100644
--- a/lib/signal.c
+++ b/lib/signal.c
@@ -27,6 +27,13 @@
 #include "villas/utils.h"
 #include "villas/node.h"
 
+int signal_init(struct signal *s)
+{
+	s->format = SIGNAL_FORMAT_UNKNOWN;
+
+	return 0;
+}
+
 int signal_destroy(struct signal *s)
 {
 	if (s->name)