diff --git a/sys/ztimer/periph_rtt.c b/sys/ztimer/periph_rtt.c
index 57ae22a7a3..f2fa4660da 100644
--- a/sys/ztimer/periph_rtt.c
+++ b/sys/ztimer/periph_rtt.c
@@ -20,6 +20,8 @@
  * @}
  */
 #include "assert.h"
+
+#include "irq.h"
 #include "periph/rtt.h"
 #include "ztimer/periph_rtt.h"