diff --git a/sys/saul_reg/saul_reg.c b/sys/saul_reg/saul_reg.c
index 40f521ebf2..729a7edf53 100644
--- a/sys/saul_reg/saul_reg.c
+++ b/sys/saul_reg/saul_reg.c
@@ -18,6 +18,7 @@
  * @}
  */
 
+#include <stddef.h>
 #include <stdio.h>
 #include <stdint.h>
 #include <string.h>
diff --git a/sys/shell/commands/sc_saul_reg.c b/sys/shell/commands/sc_saul_reg.c
index 7922292eca..b1f1adbf72 100644
--- a/sys/shell/commands/sc_saul_reg.c
+++ b/sys/shell/commands/sc_saul_reg.c
@@ -19,6 +19,7 @@
  * @}
  */
 
+#include <stddef.h>
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>