diff --git a/drivers/serial/sandbox.c b/drivers/serial/sandbox.c
index cae6c9411c..814a0f9e7f 100644
--- a/drivers/serial/sandbox.c
+++ b/drivers/serial/sandbox.c
@@ -50,7 +50,7 @@ void serial_puts(const char *str)
 int serial_getc(void)
 {
 	char buf;
-	int count;
+	ssize_t count;
 
 	count = os_read(0, &buf, 1);
 	return count == 1 ? buf : 0;