diff --git a/include/packet.h b/include/packet.h
index df2ca5e..9b68f99 100644
--- a/include/packet.h
+++ b/include/packet.h
@@ -54,6 +54,7 @@
 #define MAX_DATA_LENGTH 8192
 
 #define ADDRESS_SIZE MAX_NAME + 1 + 255 /* 1 for @, 255 for domain, defined in RFC 5321, Section 4.5.3.1.2 */
+#define CHALLENGE_SIZE 32
 #define HASH_SIZE crypto_generichash_BYTES
 #define NONCE_SIZE crypto_box_NONCEBYTES /* 24 */
 #define ADDITIONAL_SIZE crypto_box_MACBYTES /* 16 */
diff --git a/include/util.h b/include/util.h
index 47a270b..c41a18a 100644
--- a/include/util.h
+++ b/include/util.h
@@ -1,6 +1,8 @@
 #ifndef UTIL_H
 #define UTIL_H
 
+#include <stdlib.h>
+
 #define LOG_ERROR 1
 #define LOG_INFO 2
 
diff --git a/include/client/db.h b/include/zen/db.h
similarity index 100%
rename from include/client/db.h
rename to include/zen/db.h
diff --git a/include/notification.h b/include/zen/notification.h
similarity index 100%
rename from include/notification.h
rename to include/zen/notification.h
diff --git a/include/client/ui.h b/include/zen/ui.h
similarity index 100%
rename from include/client/ui.h
rename to include/zen/ui.h
diff --git a/include/client/user.h b/include/zen/user.h
similarity index 100%
rename from include/client/user.h
rename to include/zen/user.h
diff --git a/include/server/server.h b/include/zmr/zmr.h
similarity index 95%
rename from include/server/server.h
rename to include/zmr/zmr.h
index cc57854..7fafc93 100644
--- a/include/server/server.h
+++ b/include/zmr/zmr.h
@@ -1,7 +1,6 @@
 #ifndef SERVER_H_
 #define SERVER_H_
 
-#define CHALLENGE_SIZE 32
 #define MAX_CONNECTION_QUEUE 128 /* for listen() */
 #define MAX_EVENTS 64 /* Max events can be returned simulataneouly by epoll */