diff --git a/components/common/libc/src/strtoull.c b/components/common/libc/src/strtoull.c
index 2e65a43..bd63301 100644
--- a/components/common/libc/src/strtoull.c
+++ b/components/common/libc/src/strtoull.c
@@ -34,6 +34,7 @@
  * SUCH DAMAGE.
  */
 
+#include <ctype.h>
 #include <errno.h>
 #include <limits.h>
 #include <stddef.h>