diff --git a/format.c b/format.c
index 7979e970..91d78f89 100644
--- a/format.c
+++ b/format.c
@@ -1962,6 +1962,23 @@ format_cb_pane_unseen_changes(struct format_tree *ft)
 	return (NULL);
 }
 
+/* Callback for pane_key_mode. */
+static void *
+format_cb_pane_key_mode(struct format_tree *ft)
+{
+	if (ft->wp != NULL && ft->wp->screen != NULL) {
+		switch (ft->wp->screen->mode & EXTENDED_KEY_MODES) {
+		case MODE_KEYS_EXTENDED:
+			return (xstrdup("Ext 1"));
+		case MODE_KEYS_EXTENDED_2:
+			return (xstrdup("Ext 2"));
+		default:
+			return (xstrdup("VT10x"));
+		}
+	}
+	return (NULL);
+}
+
 /* Callback for pane_last. */
 static void *
 format_cb_pane_last(struct format_tree *ft)
@@ -2997,6 +3014,9 @@ static const struct format_table_entry format_table[] = {
 	{ "pane_input_off", FORMAT_TABLE_STRING,
 	  format_cb_pane_input_off
 	},
+	{ "pane_key_mode", FORMAT_TABLE_STRING,
+	  format_cb_pane_key_mode
+	},
 	{ "pane_last", FORMAT_TABLE_STRING,
 	  format_cb_pane_last
 	},
diff --git a/key-string.c b/key-string.c
index 699d460f..04f0e5bf 100644
--- a/key-string.c
+++ b/key-string.c
@@ -56,12 +56,47 @@ static const struct {
 	{ "PPage",	KEYC_PPAGE|KEYC_IMPLIED_META },
 	{ "PageUp",	KEYC_PPAGE|KEYC_IMPLIED_META },
 	{ "PgUp",	KEYC_PPAGE|KEYC_IMPLIED_META },
-	{ "Tab",	'\011' },
 	{ "BTab",	KEYC_BTAB },
 	{ "Space",	' ' },
 	{ "BSpace",	KEYC_BSPACE },
-	{ "Enter",	'\r' },
-	{ "Escape",	'\033' },
+
+	/*
+	 * C0 control characters, with the exception of Tab, Enter,
+	 * and Esc, should never appear as keys. We still render them,
+	 * so to be able to spot them in logs in case of an abnormality.
+	 */
+	{ "[NUL]",	C0_NUL },
+	{ "[SOH]",	C0_SOH },
+	{ "[STX]",	C0_STX },
+	{ "[ETX]",	C0_ETX },
+	{ "[EOT]",	C0_EOT },
+	{ "[ENQ]",	C0_ENQ },
+	{ "[ASC]",	C0_ASC },
+	{ "[BEL]",	C0_BEL },
+	{ "[BS]",	C0_BS },
+	{ "Tab",	C0_HT },
+	{ "[LF]",	C0_LF },
+	{ "[VT]",	C0_VT },
+	{ "[FF]",	C0_FF },
+	{ "Enter",	C0_CR },
+	{ "[SO]",	C0_SO },
+	{ "[SI]",	C0_SI },
+	{ "[DLE]",	C0_DLE },
+	{ "[DC1]",	C0_DC1 },
+	{ "[DC2]",	C0_DC2 },
+	{ "[DC3]",	C0_DC3 },
+	{ "[DC4]",	C0_DC4 },
+	{ "[NAK]",	C0_NAK },
+	{ "[SYN]",	C0_SYN },
+	{ "[ETB]",	C0_ETB },
+	{ "[CAN]",	C0_CAN },
+	{ "[EM]",	C0_EM },
+	{ "[SUB]",	C0_SUB },
+	{ "Escape",	C0_ESC },
+	{ "[FS]",	C0_FS },
+	{ "[GS]",	C0_GS },
+	{ "[RS]",	C0_RS },
+	{ "[US]",	C0_US },
 
 	/* Arrow keys. */
 	{ "Up",		KEYC_UP|KEYC_CURSOR|KEYC_IMPLIED_META },
@@ -206,7 +241,6 @@ key_string_get_modifiers(const char **string)
 key_code
 key_string_lookup_string(const char *string)
 {
-	static const char	*other = "!#()+,-.0123456789:;<=>'\r\t\177`/";
 	key_code		 key, modifiers;
 	u_int			 u, i;
 	struct utf8_data	 ud, *udp;
@@ -281,26 +315,6 @@ key_string_lookup_string(const char *string)
 			key &= ~KEYC_IMPLIED_META;
 	}
 
-	/* Convert the standard control keys. */
-	if (key <= 127 &&
-	    (modifiers & KEYC_CTRL) &&
-	    strchr(other, key) == NULL &&
-	    key != 9 &&
-	    key != 13 &&
-	    key != 27) {
-		if (key >= 97 && key <= 122)
-			key -= 96;
-		else if (key >= 64 && key <= 95)
-                       key -= 64;
-		else if (key == 32)
-			key = 0;
-		else if (key == 63)
-			key = 127;
-		else
-			return (KEYC_UNKNOWN);
-		modifiers &= ~KEYC_CTRL;
-	}
-
 	return (key|modifiers);
 }
 
@@ -324,10 +338,6 @@ key_string_lookup_key(key_code key, int with_flags)
 		goto out;
 	}
 
-	/* Display C-@ as C-Space. */
-	if ((key & (KEYC_MASK_KEY|KEYC_MASK_MODIFIERS)) == 0)
-		key = ' '|KEYC_CTRL;
-
 	/* Fill in the modifiers. */
 	if (key & KEYC_CTRL)
 		strlcat(out, "C-", sizeof out);
@@ -427,13 +437,8 @@ key_string_lookup_key(key_code key, int with_flags)
 		goto out;
 	}
 
-	/* Check for standard or control key. */
-	if (key <= 32) {
-		if (key == 0 || key > 26)
-			xsnprintf(tmp, sizeof tmp, "C-%c", (int)(64 + key));
-		else
-			xsnprintf(tmp, sizeof tmp, "C-%c", (int)(96 + key));
-	} else if (key >= 32 && key <= 126) {
+	/* Printable ASCII keys. */
+	if (key > 32 && key <= 126) {
 		tmp[0] = key;
 		tmp[1] = '\0';
 	} else if (key == 127)
@@ -460,8 +465,6 @@ out:
 			strlcat(out, "I", sizeof out);
 		if (saved & KEYC_BUILD_MODIFIERS)
 			strlcat(out, "B", sizeof out);
-		if (saved & KEYC_EXTENDED)
-			strlcat(out, "E", sizeof out);
 		if (saved & KEYC_SENT)
 			strlcat(out, "S", sizeof out);
 		strlcat(out, "]", sizeof out);
diff --git a/menu.c b/menu.c
index 8d7b40a2..c1f3b211 100644
--- a/menu.c
+++ b/menu.c
@@ -335,7 +335,7 @@ menu_key_cb(struct client *c, void *data, struct key_event *event)
 		c->flags |= CLIENT_REDRAWOVERLAY;
 		return (0);
 	case KEYC_PPAGE:
-	case '\002': /* C-b */
+	case 'b'|KEYC_CTRL:
 		if (md->choice < 6)
 			md->choice = 0;
 		else {
@@ -394,13 +394,13 @@ menu_key_cb(struct client *c, void *data, struct key_event *event)
 		}
 		c->flags |= CLIENT_REDRAWOVERLAY;
 		break;
-	case '\006': /* C-f */
+	case 'f'|KEYC_CTRL:
 		break;
 	case '\r':
 		goto chosen;
 	case '\033': /* Escape */
-	case '\003': /* C-c */
-	case '\007': /* C-g */
+	case 'c'|KEYC_CTRL:
+	case 'g'|KEYC_CTRL:
 	case 'q':
 		return (1);
 	}
diff --git a/mode-tree.c b/mode-tree.c
index 50e65499..efa966dc 100644
--- a/mode-tree.c
+++ b/mode-tree.c
@@ -1088,22 +1088,22 @@ mode_tree_key(struct mode_tree_data *mtd, struct client *c, key_code *key,
 	switch (*key) {
 	case 'q':
 	case '\033': /* Escape */
-	case '\007': /* C-g */
+	case 'g'|KEYC_CTRL:
 		return (1);
 	case KEYC_UP:
 	case 'k':
 	case KEYC_WHEELUP_PANE:
-	case '\020': /* C-p */
+	case 'p'|KEYC_CTRL:
 		mode_tree_up(mtd, 1);
 		break;
 	case KEYC_DOWN:
 	case 'j':
 	case KEYC_WHEELDOWN_PANE:
-	case '\016': /* C-n */
+	case 'n'|KEYC_CTRL:
 		mode_tree_down(mtd, 1);
 		break;
 	case KEYC_PPAGE:
-	case '\002': /* C-b */
+	case 'b'|KEYC_CTRL:
 		for (i = 0; i < mtd->height; i++) {
 			if (mtd->current == 0)
 				break;
@@ -1111,7 +1111,7 @@ mode_tree_key(struct mode_tree_data *mtd, struct client *c, key_code *key,
 		}
 		break;
 	case KEYC_NPAGE:
-	case '\006': /* C-f */
+	case 'f'|KEYC_CTRL:
 		for (i = 0; i < mtd->height; i++) {
 			if (mtd->current == mtd->line_size - 1)
 				break;
@@ -1155,7 +1155,7 @@ mode_tree_key(struct mode_tree_data *mtd, struct client *c, key_code *key,
 		for (i = 0; i < mtd->line_size; i++)
 			mtd->line_list[i].item->tagged = 0;
 		break;
-	case '\024': /* C-t */
+	case 't'|KEYC_CTRL:
 		for (i = 0; i < mtd->line_size; i++) {
 			if ((mtd->line_list[i].item->parent == NULL &&
 			    !mtd->line_list[i].item->no_tag) ||
@@ -1211,7 +1211,7 @@ mode_tree_key(struct mode_tree_data *mtd, struct client *c, key_code *key,
 		break;
 	case '?':
 	case '/':
-	case '\023': /* C-s */
+	case 's'|KEYC_CTRL:
 		mtd->references++;
 		status_prompt_set(c, NULL, "(search) ", "",
 		    mode_tree_search_callback, mode_tree_search_free, mtd,
diff --git a/popup.c b/popup.c
index 804dd6ef..6d126cf4 100644
--- a/popup.c
+++ b/popup.c
@@ -543,7 +543,7 @@ popup_key_cb(struct client *c, void *data, struct key_event *event)
 	}
 	if ((((pd->flags & (POPUP_CLOSEEXIT|POPUP_CLOSEEXITZERO)) == 0) ||
 	    pd->job == NULL) &&
-	    (event->key == '\033' || event->key == '\003'))
+	    (event->key == '\033' || event->key == ('c'|KEYC_CTRL)))
 		return (1);
 	if (pd->job != NULL) {
 		if (KEYC_IS_MOUSE(event->key)) {
diff --git a/screen-write.c b/screen-write.c
index 554232eb..fe58ee48 100644
--- a/screen-write.c
+++ b/screen-write.c
@@ -326,8 +326,9 @@ screen_write_reset(struct screen_write_ctx *ctx)
 	screen_write_scrollregion(ctx, 0, screen_size_y(s) - 1);
 
 	s->mode = MODE_CURSOR|MODE_WRAP;
+
 	if (options_get_number(global_options, "extended-keys") == 2)
-		s->mode |= MODE_KEXTENDED;
+		s->mode = (s->mode & ~EXTENDED_KEY_MODES)|MODE_KEYS_EXTENDED;
 
 	screen_write_clearscreen(ctx, 8);
 	screen_write_set_cursor(ctx, 0, 0);
diff --git a/screen.c b/screen.c
index de072d1a..d51af6ac 100644
--- a/screen.c
+++ b/screen.c
@@ -107,8 +107,9 @@ screen_reinit(struct screen *s)
 	s->rlower = screen_size_y(s) - 1;
 
 	s->mode = MODE_CURSOR|MODE_WRAP|(s->mode & MODE_CRLF);
+
 	if (options_get_number(global_options, "extended-keys") == 2)
-		s->mode |= MODE_KEXTENDED;
+		s->mode = (s->mode & ~EXTENDED_KEY_MODES)|MODE_KEYS_EXTENDED;
 
 	if (s->saved_grid != NULL)
 		screen_alternate_off(s, NULL, 0);
@@ -714,8 +715,10 @@ screen_mode_to_string(int mode)
 		strlcat(tmp, "ORIGIN,", sizeof tmp);
 	if (mode & MODE_CRLF)
 		strlcat(tmp, "CRLF,", sizeof tmp);
-	if (mode & MODE_KEXTENDED)
-		strlcat(tmp, "KEXTENDED,", sizeof tmp);
+	if (mode & MODE_KEYS_EXTENDED)
+		strlcat(tmp, "KEYS_EXTENDED,", sizeof tmp);
+	if (mode & MODE_KEYS_EXTENDED_2)
+		strlcat(tmp, "KEYS_EXTENDED_2,", sizeof tmp);
 	tmp[strlen(tmp) - 1] = '\0';
 	return (tmp);
 }
diff --git a/status.c b/status.c
index 4afac626..d0b4e3b5 100644
--- a/status.c
+++ b/status.c
@@ -839,19 +839,19 @@ status_prompt_translate_key(struct client *c, key_code key, key_code *new_key)
 {
 	if (c->prompt_mode == PROMPT_ENTRY) {
 		switch (key) {
-		case '\001': /* C-a */
-		case '\003': /* C-c */
-		case '\005': /* C-e */
-		case '\007': /* C-g */
-		case '\010': /* C-h */
+		case 'a'|KEYC_CTRL:
+		case 'c'|KEYC_CTRL:
+		case 'e'|KEYC_CTRL:
+		case 'g'|KEYC_CTRL:
+		case 'h'|KEYC_CTRL:
 		case '\011': /* Tab */
-		case '\013': /* C-k */
-		case '\016': /* C-n */
-		case '\020': /* C-p */
-		case '\024': /* C-t */
-		case '\025': /* C-u */
-		case '\027': /* C-w */
-		case '\031': /* C-y */
+		case 'k'|KEYC_CTRL:
+		case 'n'|KEYC_CTRL:
+		case 'p'|KEYC_CTRL:
+		case 't'|KEYC_CTRL:
+		case 'u'|KEYC_CTRL:
+		case 'w'|KEYC_CTRL:
+		case 'y'|KEYC_CTRL:
 		case '\n':
 		case '\r':
 		case KEYC_LEFT|KEYC_CTRL:
@@ -890,7 +890,7 @@ status_prompt_translate_key(struct client *c, key_code key, key_code *new_key)
 	case 'S':
 		c->prompt_mode = PROMPT_ENTRY;
 		c->flags |= CLIENT_REDRAWSTATUS;
-		*new_key = '\025'; /* C-u */
+		*new_key = 'u'|KEYC_CTRL;
 		return (1);
 	case 'i':
 	case '\033': /* Escape */
@@ -911,7 +911,7 @@ status_prompt_translate_key(struct client *c, key_code key, key_code *new_key)
 		return (1);
 	case 'C':
 	case 'D':
-		*new_key = '\013'; /* C-k */
+		*new_key = 'k'|KEYC_CTRL;
 		return (1);
 	case KEYC_BSPACE:
 	case 'X':
@@ -924,7 +924,7 @@ status_prompt_translate_key(struct client *c, key_code key, key_code *new_key)
 		*new_key = 'B'|KEYC_VI;
 		return (1);
 	case 'd':
-		*new_key = '\025'; /* C-u */
+		*new_key = 'u'|KEYC_CTRL;
 		return (1);
 	case 'e':
 		*new_key = 'e'|KEYC_VI;
@@ -939,10 +939,10 @@ status_prompt_translate_key(struct client *c, key_code key, key_code *new_key)
 		*new_key = 'W'|KEYC_VI;
 		return (1);
 	case 'p':
-		*new_key = '\031'; /* C-y */
+		*new_key = 'y'|KEYC_CTRL;
 		return (1);
 	case 'q':
-		*new_key = '\003'; /* C-c */
+		*new_key = 'c'|KEYC_CTRL;
 		return (1);
 	case 's':
 	case KEYC_DC:
@@ -966,8 +966,8 @@ status_prompt_translate_key(struct client *c, key_code key, key_code *new_key)
 	case 'k':
 		*new_key = KEYC_UP;
 		return (1);
-	case '\010' /* C-h */:
-	case '\003' /* C-c */:
+	case 'h'|KEYC_CTRL:
+	case 'c'|KEYC_CTRL:
 	case '\n':
 	case '\r':
 		return (1);
@@ -1263,28 +1263,28 @@ status_prompt_key(struct client *c, key_code key)
 process_key:
 	switch (key) {
 	case KEYC_LEFT:
-	case '\002': /* C-b */
+	case 'b'|KEYC_CTRL:
 		if (c->prompt_index > 0) {
 			c->prompt_index--;
 			break;
 		}
 		break;
 	case KEYC_RIGHT:
-	case '\006': /* C-f */
+	case 'f'|KEYC_CTRL:
 		if (c->prompt_index < size) {
 			c->prompt_index++;
 			break;
 		}
 		break;
 	case KEYC_HOME:
-	case '\001': /* C-a */
+	case 'a'|KEYC_CTRL:
 		if (c->prompt_index != 0) {
 			c->prompt_index = 0;
 			break;
 		}
 		break;
 	case KEYC_END:
-	case '\005': /* C-e */
+	case 'e'|KEYC_CTRL:
 		if (c->prompt_index != size) {
 			c->prompt_index = size;
 			break;
@@ -1295,7 +1295,7 @@ process_key:
 			goto changed;
 		break;
 	case KEYC_BSPACE:
-	case '\010': /* C-h */
+	case 'h'|KEYC_CTRL:
 		if (c->prompt_index != 0) {
 			if (c->prompt_index == size)
 				c->prompt_buffer[--c->prompt_index].size = 0;
@@ -1310,7 +1310,7 @@ process_key:
 		}
 		break;
 	case KEYC_DC:
-	case '\004': /* C-d */
+	case 'd'|KEYC_CTRL:
 		if (c->prompt_index != size) {
 			memmove(c->prompt_buffer + c->prompt_index,
 			    c->prompt_buffer + c->prompt_index + 1,
@@ -1319,17 +1319,17 @@ process_key:
 			goto changed;
 		}
 		break;
-	case '\025': /* C-u */
+	case 'u'|KEYC_CTRL:
 		c->prompt_buffer[0].size = 0;
 		c->prompt_index = 0;
 		goto changed;
-	case '\013': /* C-k */
+	case 'k'|KEYC_CTRL:
 		if (c->prompt_index < size) {
 			c->prompt_buffer[c->prompt_index].size = 0;
 			goto changed;
 		}
 		break;
-	case '\027': /* C-w */
+	case 'w'|KEYC_CTRL:
 		separators = options_get_string(oo, "word-separators");
 		idx = c->prompt_index;
 
@@ -1397,7 +1397,7 @@ process_key:
 		status_prompt_backward_word(c, separators);
 		goto changed;
 	case KEYC_UP:
-	case '\020': /* C-p */
+	case 'p'|KEYC_CTRL:
 		histstr = status_prompt_up_history(c->prompt_hindex,
 		    c->prompt_type);
 		if (histstr == NULL)
@@ -1407,7 +1407,7 @@ process_key:
 		c->prompt_index = utf8_strlen(c->prompt_buffer);
 		goto changed;
 	case KEYC_DOWN:
-	case '\016': /* C-n */
+	case 'n'|KEYC_CTRL:
 		histstr = status_prompt_down_history(c->prompt_hindex,
 		    c->prompt_type);
 		if (histstr == NULL)
@@ -1416,11 +1416,11 @@ process_key:
 		c->prompt_buffer = utf8_fromcstr(histstr);
 		c->prompt_index = utf8_strlen(c->prompt_buffer);
 		goto changed;
-	case '\031': /* C-y */
+	case 'y'|KEYC_CTRL:
 		if (status_prompt_paste(c))
 			goto changed;
 		break;
-	case '\024': /* C-t */
+	case 't'|KEYC_CTRL:
 		idx = c->prompt_index;
 		if (idx < size)
 			idx++;
@@ -1443,12 +1443,12 @@ process_key:
 		free(s);
 		break;
 	case '\033': /* Escape */
-	case '\003': /* C-c */
-	case '\007': /* C-g */
+	case 'c'|KEYC_CTRL:
+	case 'g'|KEYC_CTRL:
 		if (c->prompt_inputcb(c, c->prompt_data, NULL, 1) == 0)
 			status_prompt_clear(c);
 		break;
-	case '\022': /* C-r */
+	case 'r'|KEYC_CTRL:
 		if (~c->prompt_flags & PROMPT_INCREMENTAL)
 			break;
 		if (c->prompt_buffer[0].size == 0) {
@@ -1459,7 +1459,7 @@ process_key:
 		} else
 			prefix = '-';
 		goto changed;
-	case '\023': /* C-s */
+	case 's'|KEYC_CTRL:
 		if (~c->prompt_flags & PROMPT_INCREMENTAL)
 			break;
 		if (c->prompt_buffer[0].size == 0) {
diff --git a/tmux.1 b/tmux.1
index 3d1cb1ed..9ab65993 100644
--- a/tmux.1
+++ b/tmux.1
@@ -3733,6 +3733,10 @@ Note that aliases are expanded when a command is parsed rather than when it is
 executed, so binding an alias with
 .Ic bind-key
 will bind the expanded form.
+.It Ic copy-command Ar shell-command
+Give the command to pipe to if the
+.Ic copy-pipe
+copy mode command is used without arguments.
 .It Ic default-terminal Ar terminal
 Set the default terminal for new windows created in this session - the
 default value of the
@@ -3746,10 +3750,6 @@ be set to
 .Ql screen ,
 .Ql tmux
 or a derivative of them.
-.It Ic copy-command Ar shell-command
-Give the command to pipe to if the
-.Ic copy-pipe
-copy mode command is used without arguments.
 .It Ic escape-time Ar time
 Set the time in milliseconds for which
 .Nm
@@ -3771,22 +3771,53 @@ If enabled, the server will exit when there are no attached clients.
 .It Xo Ic extended-keys
 .Op Ic on | off | always
 .Xc
-When
-.Ic on
-or
-.Ic always ,
-the escape sequence to enable extended keys is sent to the terminal, if
-.Nm
-knows that it is supported.
-.Nm
-always recognises extended keys itself.
-If this option is
+Controls how modified keys (keys pressed together with Control, Meta, or Shift)
+are reported.
+This is the equivalent of the
+.Ic modifyOtherKeys
+.Xr xterm 1
+resource.
+.Pp
+When set to
 .Ic on ,
-.Nm
-will only forward extended keys to applications when they request them; if
+the program inside the pane can request one of two modes: mode 1 which changes
+the sequence for only keys which lack an existing well-known representation; or
+mode 2 which changes the sequence for all keys.
+When set to
 .Ic always ,
+mode 1 output is forced and the program cannot change it.
+When set to
+.Ic off ,
+this feature is disabled and only standard keys are reported.
+.Pp
 .Nm
-will always forward the keys.
+will always request extended keys itself if the terminal supports them.
+See also the
+.Ic extkeys
+feature for the
+.Ic terminal-features
+option, the
+.Ic extended-keys-format
+option and the
+.Ic pane_key_mode
+variable.
+.It Xo Ic extended-keys-format
+.Op Ic csi-u | xterm
+.Xc
+Selects one of the two possible formats for reporting modified keys to
+applications.
+This is the equivalent of the
+.Ic formatOtherKeys
+.Xr xterm 1
+resource.
+For example, C-S-a will be reported as
+.Ql ^[[27;6;65~
+when set to
+.Ic xterm ,
+and as
+.Ql ^[[65;6u
+when set to
+.Ic csi-u .
 .It Xo Ic focus-events
 .Op Ic on | off
 .Xc
@@ -5512,6 +5543,7 @@ The following variables are available, where appropriate:
 .It Li "pane_in_mode" Ta "" Ta "1 if pane is in a mode"
 .It Li "pane_index" Ta "#P" Ta "Index of pane"
 .It Li "pane_input_off" Ta "" Ta "1 if input to pane is disabled"
+.It Li "pane_key_mode" Ta "" Ta "Extended key reporting mode in this pane"
 .It Li "pane_last" Ta "" Ta "1 if last pane"
 .It Li "pane_left" Ta "" Ta "Left of pane"
 .It Li "pane_marked" Ta "" Ta "1 if this is the marked pane"
diff --git a/tmux.h b/tmux.h
index beced79d..a60f89e9 100644
--- a/tmux.h
+++ b/tmux.h
@@ -138,8 +138,7 @@ struct winlink;
 #define KEYC_IMPLIED_META    0x08000000000000ULL
 #define KEYC_BUILD_MODIFIERS 0x10000000000000ULL
 #define KEYC_VI		     0x20000000000000ULL
-#define KEYC_EXTENDED	     0x40000000000000ULL
-#define KEYC_SENT	     0x80000000000000ULL
+#define KEYC_SENT	     0x40000000000000ULL
 
 /* Masks for key bits. */
 #define KEYC_MASK_MODIFIERS  0x00f00000000000ULL
@@ -187,6 +186,42 @@ struct winlink;
  */
 typedef unsigned long long key_code;
 
+/* C0 control characters */
+enum {
+	C0_NUL,
+	C0_SOH,
+	C0_STX,
+	C0_ETX,
+	C0_EOT,
+	C0_ENQ,
+	C0_ASC,
+	C0_BEL,
+	C0_BS,
+	C0_HT,
+	C0_LF,
+	C0_VT,
+	C0_FF,
+	C0_CR,
+	C0_SO,
+	C0_SI,
+	C0_DLE,
+	C0_DC1,
+	C0_DC2,
+	C0_DC3,
+	C0_DC4,
+	C0_NAK,
+	C0_SYN,
+	C0_ETB,
+	C0_CAN,
+	C0_EM,
+	C0_SUB,
+	C0_ESC,
+	C0_FS,
+	C0_GS,
+	C0_RS,
+	C0_US
+};
+
 /* Special key codes. */
 enum {
 	/* Focus events. */
@@ -582,14 +617,16 @@ enum tty_code_code {
 #define MODE_MOUSE_ALL 0x1000
 #define MODE_ORIGIN 0x2000
 #define MODE_CRLF 0x4000
-#define MODE_KEXTENDED 0x8000
+#define MODE_KEYS_EXTENDED 0x8000
 #define MODE_CURSOR_VERY_VISIBLE 0x10000
 #define MODE_CURSOR_BLINKING_SET 0x20000
+#define MODE_KEYS_EXTENDED_2 0x40000
 
 #define ALL_MODES 0xffffff
 #define ALL_MOUSE_MODES (MODE_MOUSE_STANDARD|MODE_MOUSE_BUTTON|MODE_MOUSE_ALL)
 #define MOTION_MOUSE_MODES (MODE_MOUSE_BUTTON|MODE_MOUSE_ALL)
 #define CURSOR_MODES (MODE_CURSOR|MODE_CURSOR_BLINKING|MODE_CURSOR_VERY_VISIBLE)
+#define EXTENDED_KEY_MODES (MODE_KEYS_EXTENDED|MODE_KEYS_EXTENDED_2)
 
 /* Mouse protocol constants. */
 #define MOUSE_PARAM_MAX 0xff
diff --git a/tty-features.c b/tty-features.c
index 42f83f41..110bc1f8 100644
--- a/tty-features.c
+++ b/tty-features.c
@@ -227,7 +227,7 @@ static const struct tty_feature tty_feature_sync = {
 
 /* Terminal supports extended keys. */
 static const char *const tty_feature_extkeys_capabilities[] = {
-	"Eneks=\\E[>4;1m",
+	"Eneks=\\E[>4;2m",
 	"Dseks=\\E[>4m",
 	NULL
 };
diff --git a/tty-keys.c b/tty-keys.c
index a04d951d..9555dc31 100644
--- a/tty-keys.c
+++ b/tty-keys.c
@@ -664,7 +664,7 @@ tty_keys_next(struct tty *tty)
 	size_t			 len, size;
 	cc_t			 bspace;
 	int			 delay, expired = 0, n;
-	key_code		 key;
+	key_code		 key, onlykey;
 	struct mouse_event	 m = { 0 };
 	struct key_event	*event;
 
@@ -801,6 +801,26 @@ first_key:
 		key = (u_char)buf[0];
 		size = 1;
 	}
+
+	/* C-Space is special. */
+	if ((key & KEYC_MASK_KEY) == C0_NUL)
+		key = ' ' | KEYC_CTRL | (key & KEYC_META);
+
+	/*
+	 * Fix up all C0 control codes that don't have a dedicated key into
+	 * corresponding Ctrl keys. Convert characters in the A-Z range into
+	 * lowercase, so ^A becomes a|CTRL.
+	 */
+	onlykey = key & KEYC_MASK_KEY;
+	if (onlykey < 0x20 && onlykey != C0_BS &&
+	    onlykey != C0_HT && onlykey != C0_CR &&
+	    onlykey != C0_ESC) {
+		onlykey |= 0x40;
+		if (onlykey >= 'A' && onlykey <= 'Z')
+			onlykey |= 0x20;
+		key = onlykey | KEYC_CTRL | (key & KEYC_META);
+	}
+
 	goto complete_key;
 
 partial_key:
@@ -910,7 +930,6 @@ tty_keys_extended_key(struct tty *tty, const char *buf, size_t len,
 	char		 tmp[64];
 	cc_t		 bspace;
 	key_code	 nkey;
-	key_code	 onlykey;
 	struct utf8_data ud;
 	utf8_char        uc;
 
@@ -974,7 +993,13 @@ tty_keys_extended_key(struct tty *tty, const char *buf, size_t len,
 	/* Update the modifiers. */
 	if (modifiers > 0) {
 		modifiers--;
-		if (modifiers & 1)
+		/*
+		 * The Shift modifier may not be reported in some input modes,
+		 * which is unfortunate, as in general case determining if a
+		 * character is shifted or not requires knowing the input
+		 * keyboard layout. So we only fix up the trivial case.
+		 */
+		if (modifiers & 1 || (nkey >= 'A' && nkey <= 'Z'))
 			nkey |= KEYC_SHIFT;
 		if (modifiers & 2)
 			nkey |= (KEYC_META|KEYC_IMPLIED_META); /* Alt */
@@ -984,34 +1009,15 @@ tty_keys_extended_key(struct tty *tty, const char *buf, size_t len,
 			nkey |= (KEYC_META|KEYC_IMPLIED_META); /* Meta */
 	}
 
-	/*
-	 * Don't allow both KEYC_CTRL and as an implied modifier. Also convert
-	 * C-X into C-x and so on.
-	 */
-	if (nkey & KEYC_CTRL) {
-		onlykey = (nkey & KEYC_MASK_KEY);
-		if (onlykey < 32 &&
-		    onlykey != 9 &&
-		    onlykey != 13 &&
-		    onlykey != 27)
-			/* nothing */;
-		else if (onlykey >= 97 && onlykey <= 122)
-			onlykey -= 96;
-		else if (onlykey >= 64 && onlykey <= 95)
-			onlykey -= 64;
-		else if (onlykey == 32)
-			onlykey = 0;
-		else if (onlykey == 63)
-			onlykey = 127;
-		else
-			onlykey |= KEYC_CTRL;
-		nkey = onlykey|((nkey & KEYC_MASK_MODIFIERS) & ~KEYC_CTRL);
-	}
+	/* Convert S-Tab into Backtab. */
+	if ((nkey & KEYC_MASK_KEY) == '\011' && (nkey & KEYC_SHIFT))
+		nkey = KEYC_BTAB | (nkey & ~KEYC_MASK_KEY & ~KEYC_SHIFT);
 
 	if (log_get_level() != 0) {
 		log_debug("%s: extended key %.*s is %llx (%s)", c->name,
 		    (int)*size, buf, nkey, key_string_lookup_key(nkey, 1));
 	}
+
 	*key = nkey;
 	return (0);
 }