--- a/src/ex_cmds.c
+++ b/src/ex_cmds.c
@@ -4420,6 +4420,31 @@ do_sub(eap)
 	endcolumn = (curwin->w_curswant == MAXCOL);
     }
 
+    /* Recognize ":%s/\n//" and turn it into a join command, which is much
+     * more efficient.
+     * TODO: find a generic solution to make line-joining operations more
+     * efficient, avoid allocating a string that grows in size.
+     */
+    if (STRCMP(pat, "\\n") == 0 && STRLEN(pat) == 2
+	    && *sub == NUL
+	    && (*cmd == NUL || (cmd[1] == NUL && (*cmd == 'g' || *cmd == 'l'
+					     || *cmd == 'p' || *cmd == '#'))))
+    {
+	curwin->w_cursor.lnum = eap->line1;
+	if (*cmd == 'l')
+	    eap->flags = EXFLAG_LIST;
+	else if (*cmd == '#')
+	    eap->flags = EXFLAG_NR;
+	else if (*cmd == 'p')
+	    eap->flags = EXFLAG_PRINT;
+
+	(void)do_join(eap->line2 - eap->line1 + 1, FALSE, TRUE, FALSE);
+	sub_nlines = sub_nsubs = eap->line2 - eap->line1 + 1;
+	(void)do_sub_msg(FALSE);
+	ex_may_print(eap);
+	return;
+    }
+
     /*
      * Find trailing options.  When '&' is used, keep old options.
      */