diff --git a/doc/RELEASE-NOTES.md b/doc/RELEASE-NOTES.md
index 805a7554c..dd5e11588 100644
--- a/doc/RELEASE-NOTES.md
+++ b/doc/RELEASE-NOTES.md
@@ -107,6 +107,22 @@ in progress and may not be a stable version.
 * The [`require module` block](https://www.unrealircd.org/docs/Require_module_block)
   was only checked of one side of the link, thus partially not working.
 
+### Developers and protocol:
+* Server to server lines can now be 16384 bytes in size when
+  `PROTOCTL BIGLINES` is set. This will allow us to do things more
+  efficiently and possibly raise some other limits in the future.
+  This 16k is the size of the complete line, including sender,
+  message tags, content and \r\n. Also, in server-to-server traffic
+  we now allow 30 parameters (MAXPARA*2).  
+  The original input size limits for non-servers remain the same: the
+  complete line can be 4k+512, with the non-mtag portion limit set
+  at 512 bytes (including \r\n), and MAXPARA is still 15 as well.
+* To receive BIGLINES in a command, you need to `CommandAdd()` with
+  flags `CMD_BIGLINES`, without it you still get regular 512 max.
+  This is so, because a lot of the code does not expect longer than
+  512 bytes lines or in parameters, so we can gradually change that
+  (where needed).
+
 UnrealIRCd 6.1.0
 -----------------
 This is UnrealIRCd 6.1.0 stable. It is the direct successor to 6.0.7, there
diff --git a/include/channel.h b/include/channel.h
index f229290aa..083cfd2e1 100644
--- a/include/channel.h
+++ b/include/channel.h
@@ -33,8 +33,6 @@
  * before Dreamforge aren't safe with more than six. -Donwulff
  */
 #include "msg.h"
-#define	MAXMODEPARAMS	(MAXPARA-3)	/* Maximum modes processed */
-#define RESYNCMODES	12	/* Max modes per MODE in resync */
-#define MODEPARAMS	6	/* Max modes from user */
+#define	MAXMODEPARAMS	(MAXPARA_USER-3)	/* Maximum modes processed */
 
 #endif
diff --git a/include/msg.h b/include/msg.h
index dcae50970..3537fbf38 100644
--- a/include/msg.h
+++ b/include/msg.h
@@ -167,6 +167,7 @@
 
 #define MSG_MLOCK	"MLOCK"
 
-#define MAXPARA    	15
+#define MAXPARA    	30
+#define MAXPARA_USER	15
 
 #endif
diff --git a/include/struct.h b/include/struct.h
index 8a2edddce..a27fb1cbb 100644
--- a/include/struct.h
+++ b/include/struct.h
@@ -183,8 +183,9 @@ typedef OperPermission (*OperClassEntryEvalCallback)(OperClassACLEntryVar* varia
 #define LINKLEN		32
 #define	BUFSIZE		512	/* WARNING: *DONT* CHANGE THIS!!!! */
 #define MAXTAGSIZE	8192	/**< Maximum length of message tags (4K user + 4K server) */
-#define MAXLINELENGTH	(MAXTAGSIZE+BUFSIZE)	/**< Maximum length of a line on IRC: 4k client tags + 4k server tags + 512 bytes (IRCv3) */
-#define READBUFSIZE	MAXLINELENGTH	/* for the read buffer */
+#define MAXLINELENGTH_USER	(MAXTAGSIZE+BUFSIZE)	/**< Maximum length of a line on IRC (for non-servers): 4k client tags + 4k server tags + 512 bytes (IRCv3) */
+#define MAXLINELENGTH	16384			/**< Maximum length of a line on IRC: from servers is 16k */
+#define READBUFSIZE	MAXLINELENGTH	/**< for the read buffer */
 #define	MAXRECIPIENTS 	20
 #define	MAXSILELENGTH	NICKLEN+USERLEN+HOSTLEN+10
 #define IDLEN		12
@@ -449,6 +450,7 @@ typedef enum ClientStatus {
 #define PROTO_SJSBY	0x000020	/* SJOIN setby information (TS and nick) */
 #define PROTO_MTAGS	0x000040	/* Support message tags and big buffers */
 #define PROTO_NEXTBANS	0x000080	/* Server supports named extended bans */
+#define PROTO_BIGLINES	0x000100	/* BIGLINES support */
 
 /* For client capabilities: */
 #define CAP_INVERT	1L
@@ -614,6 +616,7 @@ typedef enum ClientStatus {
 #define SupportCLK(x)		(CHECKSERVERPROTO(x, PROTO_CLK))
 #define SupportMTAGS(x)		(CHECKSERVERPROTO(x, PROTO_MTAGS))
 #define SupportNEXTBANS(x)	(CHECKSERVERPROTO(x, PROTO_NEXTBANS))
+#define SupportBIGLINES(x)	(CHECKSERVERPROTO(x, PROTO_BIGLINES))
 
 #define SetVL(x)		((x)->local->proto |= PROTO_VL)
 #define SetSJSBY(x)		((x)->local->proto |= PROTO_SJSBY)
@@ -621,6 +624,7 @@ typedef enum ClientStatus {
 #define SetCLK(x)		((x)->local->proto |= PROTO_CLK)
 #define SetMTAGS(x)		((x)->local->proto |= PROTO_MTAGS)
 #define SetNEXTBANS(x)		((x)->local->proto |= PROTO_NEXTBANS)
+#define SetBIGLINES(x)		((x)->local->proto |= PROTO_BIGLINES)
 
 /* Dcc deny types (see src/s_extra.c) */
 #define DCCDENY_HARD	0
@@ -917,6 +921,8 @@ struct SWhois {
 #define CMD_OPER		0x0200
 /** Command is for control channel only (unrealircd.ctl socket) */
 #define CMD_CONTROL		0x0400
+/** Command is able to receive BIG lines */
+#define CMD_BIGLINES		0x0800
 
 /** Command function - used by all command handlers.
  * This is used in the code like <pre>CMD_FUNC(cmd_yourcmd)</pre> as a function definition.
diff --git a/src/modules/protoctl.c b/src/modules/protoctl.c
index b4d48c4b8..3767f8c6b 100644
--- a/src/modules/protoctl.c
+++ b/src/modules/protoctl.c
@@ -122,6 +122,10 @@ CMD_FUNC(cmd_protoctl)
 		{
 			SetNEXTBANS(client);
 		}
+		else if (!strcmp(name, "BIGLINES"))
+		{
+			SetBIGLINES(client);
+		}
 		else if (!strcmp(name, "NICKCHARS") && value)
 		{
 			if (!IsServer(client) && !IsEAuth(client) && !IsHandshake(client))
diff --git a/src/parse.c b/src/parse.c
index 321093077..e08279ffd 100644
--- a/src/parse.c
+++ b/src/parse.c
@@ -251,12 +251,13 @@ void parse(Client *cptr, char *buffer, int length)
  *               	the message has a sender, eg :xyz PRIVMSG ..
  * @param mtags  	Message tags received for this message.
  * @param mtags_bytes	The length of all message tags.
- * @param ch		The incoming line received (buffer), excluding message tags.
+ * @param line		The incoming line received (buffer), excluding message tags.
  */
-static void parse2(Client *cptr, Client **fromptr, MessageTag *mtags, int mtags_bytes, char *ch)
+static void parse2(Client *cptr, Client **fromptr, MessageTag *mtags, int mtags_bytes, char *line)
 {
 	Client *from = cptr;
 	char *s;
+	char *ch = line;
 	int len, i, numeric = 0, paramcount;
 #ifdef DEBUGMODE
 	time_t then, ticks;
@@ -267,14 +268,14 @@ static void parse2(Client *cptr, Client **fromptr, MessageTag *mtags, int mtags_
 
 	*fromptr = cptr; /* The default, unless a source is specified (and permitted) */
 
-	/* The remaining part should never be more than 510 bytes
-	 * (that is 512 minus CR LF, as specified in RFC1459 section 2.3).
+	/* In client-to-server traffic, the remaining part should
+	 * never be more than 510 bytes (that is 512 minus CR LF,
+	 * as specified in RFC1459 section 2.3).
 	 * If it is too long, then we cut it off here.
+	 * Note that there is a second check later for the IsServer() case.
 	 */
-	if (strlen(ch) > 510)
-	{
+	if (!IsServer(cptr) && (strlen(ch) > 510))
 		ch[510] = '\0';
-	}
 
 	para[0] = (char *)DEADBEEF_ADDR; /* helps us catch bugs :) */
 
@@ -355,6 +356,20 @@ static void parse2(Client *cptr, Client **fromptr, MessageTag *mtags, int mtags_
 	s = strchr(ch, ' ');	/* s -> End of the command code */
 	len = (s) ? (s - ch) : 0;
 
+	/* An early "guard": check for oversized command name
+	 * (not parameters, the actual command name being 512+ chars),
+	 * just in case... especially for BIGLINES.
+	 */
+	if (len > 512)
+	{
+		ch[510] = '\0';
+		sendto_one(from, NULL, ":%s %d %s %s :Unknown command",
+				       me.name, ERR_UNKNOWNCOMMAND,
+				       from->name, ch);
+		ircstats.is_unco++;
+		return;
+	}
+
 	if (len == 3 && isdigit(*ch) && isdigit(*(ch + 1)) && isdigit(*(ch + 2)))
 	{
 		/* Numeric (eg: 311) */
@@ -462,11 +477,26 @@ static void parse2(Client *cptr, Client **fromptr, MessageTag *mtags, int mtags_
 	   ** (about same effect as ":" has...) --msa
 	 */
 
+	/* The high MAXPARA is only for servers, so readjust here for clients... */
+	if (!IsServer(from) && (paramcount > MAXPARA_USER))
+		paramcount = MAXPARA_USER;
+
 	/* Note initially true: s==NULL || *(s-1) == '\0' !! */
 
 	i = 0;
 	if (s)
 	{
+		if (IsServer(cptr) && (!cmptr || !(cmptr->flags & CMD_BIGLINES)))
+		{
+			int slen = strlen(s);
+			if ((s-line)+slen > 510)
+			{
+				ch[510] = '\0'; /* same as check at beginning of this function */
+				if (slen > 510)
+					s[510] = '\0'; /* just in case the earlier cut was like mid-sender instead of in parameters */
+			}
+		}
+
 		/*
 		if (paramcount > MAXPARA)
 			paramcount = MAXPARA;
diff --git a/src/send.c b/src/send.c
index ff303298f..54d6dcff8 100644
--- a/src/send.c
+++ b/src/send.c
@@ -253,11 +253,33 @@ static int sendbufto_one_prepare_line(Client *to, char *msg)
 	len = strlen(p);
 	if (!len || (p[len - 1] != '\n'))
 	{
-		if (len > 510)
-			len = 510;
-		p[len++] = '\r';
-		p[len++] = '\n';
-		p[len] = '\0';
+		if (!IsServer(to) || !SupportBIGLINES(to->direction))
+		{
+			/* Normal case */
+			if (len > 510)
+				len = 510;
+			p[len++] = '\r';
+			p[len++] = '\n';
+			p[len] = '\0';
+		} else {
+			/* BIGLINES case:
+			 * - first 'if' is about the total line length,
+			 *   this is basically an optimized strlen(msg)
+			 * - the 'else' applies to non-mtags part,
+			 *   like in the 'Normal case' from above.
+			 */
+			if ((p - msg) + len > MAXLINELENGTH-3)
+			{
+				len = MAXLINELENGTH-3;
+				msg[len++] = '\r';
+				msg[len++] = '\n';
+				msg[len] = '\0';
+			} else {
+				p[len++] = '\r';
+				p[len++] = '\n';
+				p[len] = '\0';
+			}
+		}
 	}
 
 	/* Return length, that is:
diff --git a/src/serv.c b/src/serv.c
index 757ffcda6..153c51223 100644
--- a/src/serv.c
+++ b/src/serv.c
@@ -264,7 +264,7 @@ void send_proto(Client *client, ConfigItem_link *aconf)
 		me.id, (long long)TStime());
 
 	/* Third line */
-	sendto_one(client, NULL, "PROTOCTL NICKCHARS=%s CHANNELCHARS=%s",
+	sendto_one(client, NULL, "PROTOCTL NICKCHARS=%s CHANNELCHARS=%s BIGLINES",
 		charsys_get_current_languages(),
 		allowed_channelchars_valtostr(iConf.allowed_channelchars));
 }