diff --git a/src/drv_imap.c b/src/drv_imap.c
index 04794ea..24b7aa4 100644
--- a/src/drv_imap.c
+++ b/src/drv_imap.c
@@ -30,6 +30,7 @@
 #include <sys/time.h>
 #include <stdlib.h>
 #include <stdio.h>
+#include <stddef.h>
 #include <stdarg.h>
 #include <errno.h>
 #include <string.h>