diff --git a/include/nuttx/timers/timer.h b/include/nuttx/timers/timer.h
index 8e6926083c..5d11498e71 100644
--- a/include/nuttx/timers/timer.h
+++ b/include/nuttx/timers/timer.h
@@ -45,6 +45,7 @@
 #include <nuttx/compiler.h>
 #include <nuttx/irq.h>
 #include <nuttx/fs/ioctl.h>
+#include <stdbool.h>
 
 #ifdef CONFIG_TIMER