diff --git a/boards/mulle/Makefile.dep b/boards/mulle/Makefile.dep
index 800e7978c222a86f88ea68c3eb1de4bfaddc01a2..fe3cb539a2aaec903f9cf3b8900f82454e420090 100644
--- a/boards/mulle/Makefile.dep
+++ b/boards/mulle/Makefile.dep
@@ -12,6 +12,9 @@ USEMODULE += nvram
 USEMODULE += devfs
 USEMODULE += mtd_spi_nor
 
+# mulle always uses it's rtt
+USEMODULE += periph_rtt
+
 ifneq (,$(filter saul_default,$(USEMODULE)))
   USEMODULE += saul_gpio
   USEMODULE += saul_adc