diff --git a/sys/vtimer/vtimer.c b/sys/vtimer/vtimer.c
index 531666e879..8d7daf6f0a 100644
--- a/sys/vtimer/vtimer.c
+++ b/sys/vtimer/vtimer.c
@@ -35,6 +35,14 @@
 #define ENABLE_DEBUG    (0)
 #include "debug.h"
 
+#if ENABLE_DEBUG
+
+void vtimer_print_short_queue(void);
+void vtimer_print_long_queue(void);
+void vtimer_print(vtimer_t *t);
+
+#endif
+
 #define VTIMER_THRESHOLD 20UL
 #define VTIMER_BACKOFF 10UL