diff --git a/arch/sim/src/up_simsmp.c b/arch/sim/src/up_simsmp.c
index 73aaa98283a..1afdcec15f2 100644
--- a/arch/sim/src/up_simsmp.c
+++ b/arch/sim/src/up_simsmp.c
@@ -37,6 +37,7 @@
  * Included Files
  ****************************************************************************/
 
+#include <stdint.h>
 #include <pthread.h>
 #include <semaphore.h>