diff --git a/contrib/openpam/lib/pam_get_authtok.c b/contrib/openpam/lib/pam_get_authtok.c
index 8a447c3a32d..d89460f095d 100644
--- a/contrib/openpam/lib/pam_get_authtok.c
+++ b/contrib/openpam/lib/pam_get_authtok.c
@@ -37,6 +37,7 @@
 #include <sys/param.h>
 
 #include <stdlib.h>
+#include <string.h>
 
 #include <security/pam_appl.h>
 #include <security/openpam.h>