diff --git a/screen-redraw.c b/screen-redraw.c
index a10acd97..167389b4 100644
--- a/screen-redraw.c
+++ b/screen-redraw.c
@@ -368,7 +368,7 @@ screen_redraw_draw_pane_status(struct screen_redraw_ctx *ctx)
 			/* Right not visible. */
 			i = 0;
 			x = xoff - ctx->ox;
-			width = size - (xoff + size - ctx->sx);
+			width = size - x;
 		}
 
 		if (ctx->top)
@@ -628,7 +628,7 @@ screen_redraw_draw_pane(struct screen_redraw_ctx *ctx, struct window_pane *wp)
 			/* Right not visible. */
 			i = 0;
 			x = wp->xoff - ctx->ox;
-			width = wp->sx - (wp->xoff + wp->sx - ctx->sx);
+			width = ctx->sx - x;
 		}
 		log_debug("%s: %s %%%u line %u,%u at %u,%u, width %u",
 		    __func__, c->name, wp->id, i, j, x, y, width);
@@ -674,7 +674,7 @@ screen_redraw_draw_number(struct screen_redraw_ctx *ctx, struct window_pane *wp)
 	} else {
 		/* Right not visible. */
 		xoff = wp->xoff - ctx->ox;
-		sx = wp->sx - (wp->xoff + wp->sx - ctx->sx);
+		sx = wp->sx - xoff;
 	}
 	if (wp->yoff >= ctx->oy && wp->yoff + wp->sy <= ctx->oy + ctx->sy) {
 		/* All visible. */
@@ -692,7 +692,7 @@ screen_redraw_draw_number(struct screen_redraw_ctx *ctx, struct window_pane *wp)
 	} else {
 		/* Bottom not visible. */
 		yoff = wp->yoff - ctx->oy;
-		sy = wp->sy - (wp->yoff + wp->sy - ctx->sy);
+		sy = wp->sy - yoff;
 	}
 
 	if (ctx->top)
diff --git a/tty.c b/tty.c
index 10ae1617..bf4c1424 100644
--- a/tty.c
+++ b/tty.c
@@ -936,8 +936,13 @@ tty_clamp_line(struct tty *tty, const struct tty_ctx *ctx, u_int px, u_int py,
 		/* Right not visible. */
 		*i = 0;
 		*x = (ctx->xoff + px) - ctx->ox;
-		*rx = nx - ((ctx->xoff + px) + nx - ctx->sx);
+		*rx = ctx->sx - *x;
 	}
+	if (*rx > nx)
+		fatalx("%s: x too big, %u > %u", __func__, *rx, nx);
+	if (nx > *rx)
+		*rx = nx;
+
 	return (1);
 }
 
@@ -1028,8 +1033,13 @@ tty_clamp_area(struct tty *tty, const struct tty_ctx *ctx, u_int px, u_int py,
 		/* Right not visible. */
 		*i = 0;
 		*x = (ctx->xoff + px) - ctx->ox;
-		*rx = nx - ((ctx->xoff + px) + nx - ctx->sx);
+		*rx = ctx->sx - *x;
 	}
+	if (*rx > nx)
+		fatalx("%s: x too big, %u > %u", __func__, *rx, nx);
+	if (nx > *rx)
+		*rx = nx;
+
 	if (yoff >= ctx->oy && yoff + ny <= ctx->oy + ctx->sy) {
 		/* All visible. */
 		*j = 0;
@@ -1049,8 +1059,13 @@ tty_clamp_area(struct tty *tty, const struct tty_ctx *ctx, u_int px, u_int py,
 		/* Right not visible. */
 		*j = 0;
 		*y = (ctx->yoff + py) - ctx->oy;
-		*ry = ny - ((ctx->yoff + py) + ny - ctx->sy);
+		*ry = ctx->sy - *y;
 	}
+	if (*ry > ny)
+		fatalx("%s: y too big, %u > %u", __func__, *ry, ny);
+	if (ny > *ry)
+		*ry = ny;
+
 	return (1);
 }