diff --git a/src/system/libroot/posix/sys/itimer.c b/src/system/libroot/posix/sys/itimer.c
index b2f1d736fd..f2802d05a5 100644
--- a/src/system/libroot/posix/sys/itimer.c
+++ b/src/system/libroot/posix/sys/itimer.c
@@ -6,6 +6,7 @@
 
 #include <OS.h>
 
+#include <errno.h>
 #include <sys/time.h>
 #include <string.h>