diff --git a/screen-display.c b/screen-display.c
index d786c19c..66cd4e1d 100644
--- a/screen-display.c
+++ b/screen-display.c
@@ -1,4 +1,4 @@
-/* $Id: screen-display.c,v 1.11 2007-12-06 10:16:36 nicm Exp $ */
+/* $Id: screen-display.c,v 1.12 2007-12-06 10:36:01 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicm@users.sourceforge.net>
@@ -34,8 +34,10 @@ screen_display_set_cell(
 void
 screen_display_make_lines(struct screen *s, u_int py, u_int ny)
 {
-	if (ny == 0 || !screen_in_y(s, py) || !screen_in_y(s, py + ny - 1))
+	if (ny == 0 || !screen_in_y(s, py) || !screen_in_y(s, py + ny - 1)) {
+		SCREEN_DEBUG2(s, py, ny);
 		return;
+	}
 	screen_make_lines(s, screen_y(s, py), ny);
 }
 
@@ -43,8 +45,10 @@ screen_display_make_lines(struct screen *s, u_int py, u_int ny)
 void
 screen_display_free_lines(struct screen *s, u_int py, u_int ny)
 {
-	if (ny == 0 || !screen_in_y(s, py) || !screen_in_y(s, py + ny - 1))
+	if (ny == 0 || !screen_in_y(s, py) || !screen_in_y(s, py + ny - 1)) {
+		SCREEN_DEBUG2(s, py, ny);
 		return;
+	}
 	screen_free_lines(s, screen_y(s, py), ny);
 }
 
@@ -52,10 +56,14 @@ screen_display_free_lines(struct screen *s, u_int py, u_int ny)
 void
 screen_display_move_lines(struct screen *s, u_int dy, u_int py, u_int ny)
 {
-	if (ny == 0 || !screen_in_y(s, py) || !screen_in_y(s, py + ny - 1))
+	if (ny == 0 || !screen_in_y(s, py) || !screen_in_y(s, py + ny - 1)) {
+		SCREEN_DEBUG3(s, dy, py, ny);
 		return;
-	if (!screen_in_y(s, dy) || !screen_in_y(s, dy + ny - 1) || dy == py)
+	}
+	if (!screen_in_y(s, dy) || !screen_in_y(s, dy + ny - 1) || dy == py) {
+		SCREEN_DEBUG3(s, dy, py, ny);
 		return;
+	}
 	screen_move_lines(s, screen_y(s, dy), screen_y(s, py), ny);
 }
 
@@ -64,12 +72,18 @@ void
 screen_display_fill_area(struct screen *s, u_int px, u_int py,
     u_int nx, u_int ny, u_char data, u_char attr, u_char colr)
 {
-	if (nx == 0 || ny == 0)
+	if (nx == 0 || ny == 0) {
+		SCREEN_DEBUG4(s, px, py, nx, ny);
 		return;
-	if (!screen_in_x(s, px) || !screen_in_y(s, py))
+	}
+	if (!screen_in_x(s, px) || !screen_in_y(s, py)) {
+		SCREEN_DEBUG4(s, px, py, nx, ny);
 		return;
-	if (!screen_in_x(s, px + nx - 1) || !screen_in_y(s, py + ny - 1))
+	}
+	if (!screen_in_x(s, px + nx - 1) || !screen_in_y(s, py + ny - 1)) {
+		SCREEN_DEBUG4(s, px, py, nx, ny);
 		return;
+	}
 	screen_fill_area(
 	    s, screen_x(s, px), screen_y(s, py), nx, ny, data, attr, colr);
 }
@@ -163,15 +177,21 @@ screen_display_scroll_region_down(struct screen *s)
 void
 screen_display_insert_lines(struct screen *s, u_int py, u_int ny)
 {
-	if (!screen_in_y(s, py))
+	if (!screen_in_y(s, py)) {
+		SCREEN_DEBUG2(s, py, ny);
 		return;
-	if (ny == 0)
+	}
+	if (ny == 0) {
+		SCREEN_DEBUG2(s, py, ny);
 		return;
+	}
 
 	if (py + ny > screen_last_y(s))
 		ny = screen_size_y(s) - py;
-	if (ny == 0)
+	if (ny == 0) {
+		SCREEN_DEBUG2(s, py, ny);
 		return;
+	}
 
 	/*
 	 * Insert range of ny lines at py:
@@ -200,15 +220,21 @@ screen_display_insert_lines(struct screen *s, u_int py, u_int ny)
 void
 screen_display_insert_lines_region(struct screen *s, u_int py, u_int ny)
 {
-	if (!screen_in_region(s, py))
+	if (!screen_in_region(s, py)) {
+		SCREEN_DEBUG2(s, py, ny);
 		return;
-	if (ny == 0)
+	}
+	if (ny == 0) {
+		SCREEN_DEBUG2(s, py, ny);
 		return;
+	}
 
 	if (py + ny > s->rlower)
 		ny = (s->rlower + 1) - py;
-	if (ny == 0)
+	if (ny == 0) {
+		SCREEN_DEBUG2(s, py, ny);
 		return;
+	}
 
 	/*
 	 * Insert range of ny lines at py:
@@ -237,15 +263,21 @@ screen_display_insert_lines_region(struct screen *s, u_int py, u_int ny)
 void
 screen_display_delete_lines(struct screen *s, u_int py, u_int ny)
 {
-	if (!screen_in_y(s, py))
+	if (!screen_in_y(s, py)) {
+		SCREEN_DEBUG2(s, py, ny);
 		return;
-	if (ny == 0)
+	}
+	if (ny == 0) {
+		SCREEN_DEBUG2(s, py, ny);
 		return;
+	}
 
 	if (py + ny > screen_last_y(s))
 		ny = screen_size_y(s) - py;
-	if (ny == 0)
+	if (ny == 0) {
+		SCREEN_DEBUG2(s, py, ny);
 		return;
+	}
 
 	/*
 	 * Delete range of ny lines at py:
@@ -274,10 +306,14 @@ screen_display_delete_lines(struct screen *s, u_int py, u_int ny)
 void
 screen_display_delete_lines_region(struct screen *s, u_int py, u_int ny)
 {
-	if (!screen_in_region(s, py))
+	if (!screen_in_region(s, py)) {
+		SCREEN_DEBUG2(s, py, ny);
 		return;
-	if (ny == 0)
+	}
+	if (ny == 0) {
+		SCREEN_DEBUG2(s, py, ny);
 		return;
+	}
 
 	if (py + ny > s->rlower)
 		ny = (s->rlower + 1) - py;
@@ -313,8 +349,10 @@ screen_display_insert_characters(struct screen *s, u_int px, u_int py, u_int nx)
 {
 	u_int	mx;
 
-	if (!screen_in_x(s, px) || !screen_in_y(s, py))
+	if (!screen_in_x(s, px) || !screen_in_y(s, py)) {
+		SCREEN_DEBUG3(s, px, py, nx);
 		return;
+	}
 
 	if (px + nx > screen_last_x(s))
 		nx = screen_last_x(s) - px;
@@ -350,8 +388,10 @@ screen_display_delete_characters(struct screen *s, u_int px, u_int py, u_int nx)
 {
 	u_int	mx;
 
-	if (!screen_in_x(s, px) || !screen_in_y(s, py))
+	if (!screen_in_x(s, px) || !screen_in_y(s, py)) {
+		SCREEN_DEBUG3(s, px, py, nx);
 		return;
+	}
 
 	if (px + nx > screen_last_x(s))
 		nx = screen_last_x(s) - px;
@@ -389,12 +429,18 @@ screen_display_copy_area(struct screen *dst, struct screen *src,
 	u_int	i, j;
 	u_char	data, attr, colr;
 
-	if (nx == 0 || ny == 0)
+	if (nx == 0 || ny == 0) {
+		SCREEN_DEBUG4(dst, px, py, nx, ny);
 		return;
-	if (!screen_in_x(dst, px) || !screen_in_y(dst, py))
-		return;
-	if (!screen_in_x(dst, px + nx - 1) || !screen_in_y(dst, py + ny - 1))
+	}
+	if (!screen_in_x(dst, px) || !screen_in_y(dst, py)) {
+		SCREEN_DEBUG4(dst, px, py, nx, ny);
+		return; 
+	}
+	if (!screen_in_x(dst, px + nx - 1) || !screen_in_y(dst, py + ny - 1)) {
+		SCREEN_DEBUG4(dst, px, py, nx, ny);
 		return;
+	}
 
 	for (i = py; i < py + ny; i++) {
 		for (j = px; j < px + nx; j++) {
diff --git a/screen-write.c b/screen-write.c
index eee14c72..549242e8 100644
--- a/screen-write.c
+++ b/screen-write.c
@@ -1,4 +1,4 @@
-/* $Id: screen-write.c,v 1.2 2007-12-06 10:16:36 nicm Exp $ */
+/* $Id: screen-write.c,v 1.3 2007-12-06 10:36:01 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicm@users.sourceforge.net>
@@ -22,11 +22,15 @@
 
 #include "tmux.h"
 
-#define screen_write_limit(v, lower, upper) do {	\
-	if (v < lower)					\
-		v = lower;				\
-	if (v > upper)					\
-		v = upper;				\
+#define screen_write_limit(s, v, lower, upper) do {			\
+	if (v < lower) {						\
+		v = lower;						\
+		SCREEN_DEBUG3(s, v, lower, upper);			\
+	}								\
+	if (v > upper) {						\
+		v = upper;						\
+		SCREEN_DEBUG3(s, v, lower, upper);			\
+	}								\
 } while (0)
 
 /* Initialise writing with a window. */
@@ -104,8 +108,10 @@ screen_write_put_character(struct screen_write_ctx *ctx, u_char ch)
 		if (ctx->write != NULL)
 			ctx->write(ctx->data, TTY_CHARACTER, '\r');
 		screen_write_cursor_down_scroll(ctx);
-	} else if (!screen_in_x(s, s->cx) || !screen_in_y(s, s->cy))
+	} else if (!screen_in_x(s, s->cx) || !screen_in_y(s, s->cy)) {
+		SCREEN_DEBUG(s);
 		return;
+	}
 
 	screen_display_set_cell(s, s->cx, s->cy, ch, s->attr, s->colr);
 	s->cx++;
@@ -188,10 +194,12 @@ screen_write_set_region(struct screen_write_ctx *ctx, u_int upper, u_int lower)
 {
 	struct screen	*s = ctx->s;
 
-	screen_write_limit(upper, 0, screen_last_y(s));
-	screen_write_limit(lower, 0, screen_last_y(s));
-	if (upper > lower)
+	screen_write_limit(s, upper, 0, screen_last_y(s));
+	screen_write_limit(s, lower, 0, screen_last_y(s));
+	if (upper > lower) {
+		SCREEN_DEBUG2(s,  upper, lower);
 		return;
+	}
 
 	/* Cursor moves to top-left. */
 	s->cx = 0;
@@ -240,7 +248,7 @@ screen_write_cursor_up(struct screen_write_ctx *ctx, u_int n)
 {
 	struct screen	*s = ctx->s;
 
-	screen_write_limit(n, 1, screen_above_y(s, s->cy) - 1);
+	screen_write_limit(s, n, 1, screen_above_y(s, s->cy) - 1);
 
 	s->cy -= n;
 
@@ -254,7 +262,7 @@ screen_write_cursor_down(struct screen_write_ctx *ctx, u_int n)
 {
 	struct screen	*s = ctx->s;
 
-	screen_write_limit(n, 1, screen_below_y(s, s->cy) - 1);
+	screen_write_limit(s, n, 1, screen_below_y(s, s->cy) - 1);
 
 	s->cy += n;
 
@@ -268,7 +276,7 @@ screen_write_cursor_left(struct screen_write_ctx *ctx, u_int n)
 {
 	struct screen	*s = ctx->s;
 
-	screen_write_limit(n, 1, screen_left_x(s, s->cx) - 1);
+	screen_write_limit(s, n, 1, screen_left_x(s, s->cx) - 1);
 
 	s->cx -= n;
 
@@ -282,7 +290,7 @@ screen_write_cursor_right(struct screen_write_ctx *ctx, u_int n)
 {
 	struct screen	*s = ctx->s;
 
-	screen_write_limit(n, 1, screen_right_x(s, s->cx) - 1);
+	screen_write_limit(s, n, 1, screen_right_x(s, s->cx) - 1);
 
 	s->cx += n;
 
@@ -296,7 +304,7 @@ screen_write_delete_lines(struct screen_write_ctx *ctx, u_int n)
 {
 	struct screen	*s = ctx->s;
 
-	screen_write_limit(n, 1, screen_below_y(s, s->cy));
+	screen_write_limit(s, n, 1, screen_below_y(s, s->cy));
 
 	if (s->cy < s->rupper || s->cy > s->rlower)
 		screen_display_delete_lines(s, s->cy, n);
@@ -313,7 +321,7 @@ screen_write_delete_characters(struct screen_write_ctx *ctx, u_int n)
 {
 	struct screen	*s = ctx->s;
 
-	screen_write_limit(n, 1, screen_right_x(s, s->cx));
+	screen_write_limit(s, n, 1, screen_right_x(s, s->cx));
 
 	screen_display_delete_characters(s, s->cx, s->cy, n);
 
@@ -327,7 +335,7 @@ screen_write_insert_lines(struct screen_write_ctx *ctx, u_int n)
 {
 	struct screen	*s = ctx->s;
 
-	screen_write_limit(n, 1, screen_below_y(s, s->cy));
+	screen_write_limit(s, n, 1, screen_below_y(s, s->cy));
 
 	if (s->cy < s->rupper || s->cy > s->rlower)
 		screen_display_insert_lines(s, s->cy, n);
@@ -344,7 +352,7 @@ screen_write_insert_characters(struct screen_write_ctx *ctx, u_int n)
 {
  	struct screen	*s = ctx->s;
 
-	screen_write_limit(n, 1, screen_right_x(s, s->cx));
+	screen_write_limit(s, n, 1, screen_right_x(s, s->cx));
 
 	screen_display_insert_characters(s, s->cx, s->cy, n);
 
@@ -358,8 +366,8 @@ screen_write_move_cursor(struct screen_write_ctx *ctx, u_int n, u_int m)
 {
  	struct screen	*s = ctx->s;
 
-	screen_write_limit(n, 0, screen_last_x(s));
-	screen_write_limit(m, 0, screen_last_y(s));
+	screen_write_limit(s, n, 0, screen_last_x(s));
+	screen_write_limit(s, m, 0, screen_last_y(s));
 
 	s->cx = n;
 	s->cy = m;
@@ -499,8 +507,8 @@ screen_write_copy_area(struct screen_write_ctx *ctx,
 	struct screen_redraw_ctx	rctx;
 	int				saved_mode;
 
-	screen_write_limit(nx, 1, screen_right_x(s, s->cx));
-	screen_write_limit(ny, 1, screen_below_y(s, s->cy));
+	screen_write_limit(s, nx, 1, screen_right_x(s, s->cx));
+	screen_write_limit(s, ny, 1, screen_below_y(s, s->cy));
 
 	screen_display_copy_area(ctx->s, src, s->cx, s->cy, nx, ny, ox, oy);
 
diff --git a/tmux.h b/tmux.h
index 90d4549f..01b44996 100644
--- a/tmux.h
+++ b/tmux.h
@@ -1,4 +1,4 @@
-/* $Id: tmux.h,v 1.110 2007-12-06 10:04:42 nicm Exp $ */
+/* $Id: tmux.h,v 1.111 2007-12-06 10:36:01 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicm@users.sourceforge.net>
@@ -428,6 +428,29 @@ struct screen_write_ctx {
 #define screen_below_y(s, y) \
 	((y) < screen_size_y(s) ? screen_size_y(s) - (y) : 0)
 
+#define SCREEN_DEBUG(s) do {						\
+	log_warnx("%s: cx=%u,cy=%u sx=%u,sy=%u", __func__,		\
+	    s->cx, s->cy, screen_size_x(s), screen_size_y(s));		\
+} while (0)
+#define SCREEN_DEBUG1(s, n) do {					\
+	log_warnx("%s: cx=%u,cy=%u sx=%u,sy=%u n=%u m=%u", __func__,	\
+	    s->cx, s->cy, screen_size_x(s), screen_size_y(s), n);	\
+} while (0)
+#define SCREEN_DEBUG2(s, n, m) do {					\
+	log_warnx("%s: cx=%u,cy=%u sx=%u,sy=%u n=%u m=%u", __func__,	\
+	    s->cx, s->cy, screen_size_x(s), screen_size_y(s), n, m);	\
+} while (0)
+#define SCREEN_DEBUG3(s, n, m, o) do {					\
+	log_warnx("%s: cx=%u,cy=%u sx=%u,sy=%u n=%u m=%u o=%u",		\
+	    __func__, s->cx, s->cy, screen_size_x(s), screen_size_y(s), \
+	    n, m, o);							\
+} while (0)
+#define SCREEN_DEBUG4(s, n, m, o, p) do {				\
+	log_warnx("%s: cx=%u,cy=%u sx=%u,sy=%u n=%u m=%u o=%u p=%u",	\
+	    __func__, s->cx, s->cy, screen_size_x(s), screen_size_y(s), \
+	    n, m, o, p);					       	\
+} while (0)
+
 /* Screen default contents. */
 #define SCREEN_DEFDATA ' '
 #define SCREEN_DEFATTR 0