diff --git a/src/sna/sna_accel.c b/src/sna/sna_accel.c
index 13f91c28..60e1a809 100644
--- a/src/sna/sna_accel.c
+++ b/src/sna/sna_accel.c
@@ -5200,15 +5200,15 @@ sna_fill_spans__gpu(DrawablePtr drawable, GCPtr gc, int n,
 		}
 
 		if (gc->fillStyle == FillTiled) {
-			sna_poly_fill_rect_tiled_blt(drawable,
-						     data->bo, NULL,
-						     gc, n, rect,
-						     &data->region.extents, 2);
+			(void)sna_poly_fill_rect_tiled_blt(drawable,
+							   data->bo, NULL,
+							   gc, n, rect,
+							   &data->region.extents, 2);
 		} else {
-			sna_poly_fill_rect_stippled_blt(drawable,
-							data->bo, NULL,
-							gc, n, rect,
-							&data->region.extents, 2);
+			(void)sna_poly_fill_rect_stippled_blt(drawable,
+							      data->bo, NULL,
+							      gc, n, rect,
+							      &data->region.extents, 2);
 		}
 		free (rect);
 	}
@@ -6212,8 +6212,12 @@ sna_poly_zero_line_blt(DrawablePtr drawable,
 				}
 				b->x2++;
 				b->y2++;
-				if (oc1 | oc2)
-					box_intersect(b, extents);
+				if (oc1 | oc2) {
+					bool intersects;
+
+					intersects = box_intersect(b, extents);
+					assert(intersects);
+				}
 				if (++b == last_box) {
 					ret = &&rectangle_continue;
 					goto *jump;
diff --git a/src/sna/sna_blt.c b/src/sna/sna_blt.c
index 4a9dbff9..7690afed 100644
--- a/src/sna/sna_blt.c
+++ b/src/sna/sna_blt.c
@@ -1205,16 +1205,18 @@ blt_put_composite(struct sna *sna,
 			    data, pitch);
 	} else {
 		BoxRec box;
+		bool ok;
 
 		box.x1 = dst_x;
 		box.y1 = dst_y;
 		box.x2 = dst_x + r->width;
 		box.y2 = dst_y + r->height;
 
-		sna_write_boxes(sna, dst,
-				dst_priv->gpu_bo, 0, 0,
-				data, pitch, src_x, src_y,
-				&box, 1);
+		ok = sna_write_boxes(sna, dst,
+				     dst_priv->gpu_bo, 0, 0,
+				     data, pitch, src_x, src_y,
+				     &box, 1);
+		assert(ok);
 	}
 }
 
@@ -1242,12 +1244,15 @@ fastcall static void blt_put_composite_box(struct sna *sna,
 		sna_replace(sna, op->dst.pixmap, &dst_priv->gpu_bo,
 			    data, pitch);
 	} else {
-		sna_write_boxes(sna, op->dst.pixmap,
-				op->dst.bo, op->dst.x, op->dst.y,
-				src->devPrivate.ptr,
-				src->devKind,
-				op->u.blt.sx, op->u.blt.sy,
-				box, 1);
+		bool ok;
+
+		ok = sna_write_boxes(sna, op->dst.pixmap,
+				     op->dst.bo, op->dst.x, op->dst.y,
+				     src->devPrivate.ptr,
+				     src->devKind,
+				     op->u.blt.sx, op->u.blt.sy,
+				     box, 1);
+		assert(ok);
 	}
 }
 
@@ -1276,12 +1281,15 @@ static void blt_put_composite_boxes(struct sna *sna,
 		sna_replace(sna, op->dst.pixmap, &dst_priv->gpu_bo,
 			    data, pitch);
 	} else {
-		sna_write_boxes(sna, op->dst.pixmap,
-				op->dst.bo, op->dst.x, op->dst.y,
-				src->devPrivate.ptr,
-				src->devKind,
-				op->u.blt.sx, op->u.blt.sy,
-				box, n);
+		bool ok;
+
+		ok = sna_write_boxes(sna, op->dst.pixmap,
+				     op->dst.bo, op->dst.x, op->dst.y,
+				     src->devPrivate.ptr,
+				     src->devKind,
+				     op->u.blt.sx, op->u.blt.sy,
+				     box, n);
+		assert(ok);
 	}
 }
 
diff --git a/src/sna/sna_composite.c b/src/sna/sna_composite.c
index 85453d3d..c14af3c9 100644
--- a/src/sna/sna_composite.c
+++ b/src/sna/sna_composite.c
@@ -845,17 +845,19 @@ sna_composite_rectangles(CARD8		 op,
 			       pixmap->drawable.width, pixmap->drawable.height);
 		priv->undamaged = false;
 		if (op <= PictOpSrc) {
-			priv->clear = true;
+			bool ok = true;
+
 			priv->clear_color = 0;
 			if (op == PictOpSrc)
-				sna_get_pixel_from_rgba(&priv->clear_color,
-							color->red,
-							color->green,
-							color->blue,
-							color->alpha,
-							dst->format);
-			DBG(("%s: marking clear [%08x]\n",
-			     __FUNCTION__, priv->clear_color));
+				ok = sna_get_pixel_from_rgba(&priv->clear_color,
+							     color->red,
+							     color->green,
+							     color->blue,
+							     color->alpha,
+							     dst->format);
+			priv->clear = ok;
+			DBG(("%s: marking clear [%08x]? %d\n",
+			     __FUNCTION__, priv->clear_color, ok));
 		}
 	}
 	if (!DAMAGE_IS_ALL(priv->gpu_damage)) {
diff --git a/src/sna/sna_render.c b/src/sna/sna_render.c
index 199fdd58..49f7c5e8 100644
--- a/src/sna/sna_render.c
+++ b/src/sna/sna_render.c
@@ -1886,12 +1886,15 @@ sna_render_composite_redirect_done(struct sna *sna,
 		assert(op->dst.bo != t->real_bo);
 
 		if (t->box.x2 > t->box.x1) {
+			bool ok;
+
 			DBG(("%s: copying temporary to dst\n", __FUNCTION__));
-			sna_blt_copy_boxes(sna, GXcopy,
-					   op->dst.bo, -t->box.x1, -t->box.y1,
-					   t->real_bo, 0, 0,
-					   op->dst.pixmap->drawable.bitsPerPixel,
-					   &t->box, 1);
+			ok = sna_blt_copy_boxes(sna, GXcopy,
+						op->dst.bo, -t->box.x1, -t->box.y1,
+						t->real_bo, 0, 0,
+						op->dst.pixmap->drawable.bitsPerPixel,
+						&t->box, 1);
+			assert(ok);
 		}
 		if (t->damage) {
 			DBG(("%s: combining damage, offset=(%d, %d)\n",