diff --git a/src/tsm_screen.c b/src/tsm_screen.c
index 1acead1..9242caf 100644
--- a/src/tsm_screen.c
+++ b/src/tsm_screen.c
@@ -869,18 +869,30 @@ void tsm_screen_reset(struct tsm_screen *con)
 
 void tsm_screen_set_flags(struct tsm_screen *con, unsigned int flags)
 {
+	unsigned int old;
+
 	if (!con || !flags)
 		return;
 
+	old = con->flags;
 	con->flags |= flags;
+
+	if (!(old & TSM_SCREEN_ALTERNATE) && (flags & TSM_SCREEN_ALTERNATE))
+		con->lines = con->alt_lines;
 }
 
 void tsm_screen_reset_flags(struct tsm_screen *con, unsigned int flags)
 {
+	unsigned int old;
+
 	if (!con || !flags)
 		return;
 
+	old = con->flags;
 	con->flags &= ~flags;
+
+	if ((old & TSM_SCREEN_ALTERNATE) && (flags & TSM_SCREEN_ALTERNATE))
+		con->lines = con->main_lines;
 }
 
 unsigned int tsm_screen_get_flags(struct tsm_screen *con)
diff --git a/src/tsm_screen.h b/src/tsm_screen.h
index 9e3807d..e294630 100644
--- a/src/tsm_screen.h
+++ b/src/tsm_screen.h
@@ -71,6 +71,7 @@ typedef void (*tsm_log_t) (const char *file,
 #define TSM_SCREEN_INVERSE	0x08
 #define TSM_SCREEN_HIDE_CURSOR	0x10
 #define TSM_SCREEN_FIXED_POS	0x20
+#define TSM_SCREEN_ALTERNATE	0x40
 
 #define TSM_SCREEN_OPT_RENDER_TIMING	0x01