diff --git a/src/sna/gen3_render.c b/src/sna/gen3_render.c
index c9c18fee..ecf3e8aa 100644
--- a/src/sna/gen3_render.c
+++ b/src/sna/gen3_render.c
@@ -1977,6 +1977,7 @@ inline static int gen3_get_rectangles(struct sna *sna,
 	DBG(("%s: want=%d, rem=%d\n",
 	     __FUNCTION__, want*op->floats_per_rect, vertex_space(sna)));
 
+	assert(want);
 	assert(sna->render.vertex_index * op->floats_per_vertex == sna->render.vertex_used);
 
 start:
@@ -1993,6 +1994,8 @@ start:
 		     !gen3_rectangle_begin(sna, op)))
 		goto flush;
 
+	assert(op->floats_per_rect >= vertex_space(sna));
+	assert(rem <= vertex_space(sna));
 	if (want > 1 && want * op->floats_per_rect > rem)
 		want = rem / op->floats_per_rect;
 	sna->render.vertex_index += 3*want;
diff --git a/src/sna/gen4_render.c b/src/sna/gen4_render.c
index 64077a2d..00518d4c 100644
--- a/src/sna/gen4_render.c
+++ b/src/sna/gen4_render.c
@@ -642,6 +642,8 @@ inline static int gen4_get_rectangles(struct sna *sna,
 {
 	int rem;
 
+	assert(want);
+
 start:
 	rem = vertex_space(sna);
 	if (unlikely(rem < op->floats_per_rect)) {
@@ -656,6 +658,8 @@ start:
 		     !gen4_rectangle_begin(sna, op)))
 		goto flush;
 
+	assert(op->floats_per_rect >= vertex_space(sna));
+	assert(rem <= vertex_space(sna));
 	if (want > 1 && want * op->floats_per_rect > rem)
 		want = rem / op->floats_per_rect;
 
@@ -2034,6 +2038,7 @@ gen4_render_composite_spans_boxes__thread(struct sna *sna,
 	     __FUNCTION__, nbox,
 	     op->base.src.offset[0], op->base.src.offset[1],
 	     op->base.dst.x, op->base.dst.y));
+	assert(nbox);
 
 	sna_vertex_lock(&sna->render);
 	do {
diff --git a/src/sna/gen5_render.c b/src/sna/gen5_render.c
index 6e119963..483ca4b1 100644
--- a/src/sna/gen5_render.c
+++ b/src/sna/gen5_render.c
@@ -628,6 +628,8 @@ inline static int gen5_get_rectangles(struct sna *sna,
 {
 	int rem;
 
+	assert(want);
+
 start:
 	rem = vertex_space(sna);
 	if (unlikely(rem < op->floats_per_rect)) {
@@ -642,6 +644,8 @@ start:
 		     !gen5_rectangle_begin(sna, op)))
 		goto flush;
 
+	assert(op->floats_per_rect >= vertex_space(sna));
+	assert(rem <= vertex_space(sna));
 	if (want > 1 && want * op->floats_per_rect > rem)
 		want = rem / op->floats_per_rect;
 
diff --git a/src/sna/gen6_render.c b/src/sna/gen6_render.c
index 3855f044..60958e16 100644
--- a/src/sna/gen6_render.c
+++ b/src/sna/gen6_render.c
@@ -1177,6 +1177,8 @@ inline static int gen6_get_rectangles(struct sna *sna,
 {
 	int rem;
 
+	assert(want);
+
 start:
 	rem = vertex_space(sna);
 	if (unlikely(rem < op->floats_per_rect)) {
@@ -1191,6 +1193,8 @@ start:
 		     !gen6_rectangle_begin(sna, op)))
 		goto flush;
 
+	assert(op->floats_per_rect >= vertex_space(sna));
+	assert(rem <= vertex_space(sna));
 	if (want > 1 && want * op->floats_per_rect > rem)
 		want = rem / op->floats_per_rect;
 
diff --git a/src/sna/gen7_render.c b/src/sna/gen7_render.c
index d9bb18d3..d169388b 100644
--- a/src/sna/gen7_render.c
+++ b/src/sna/gen7_render.c
@@ -1322,6 +1322,8 @@ inline static int gen7_get_rectangles(struct sna *sna,
 {
 	int rem;
 
+	assert(want);
+
 start:
 	rem = vertex_space(sna);
 	if (unlikely(rem < op->floats_per_rect)) {
@@ -1336,6 +1338,8 @@ start:
 		     !gen7_rectangle_begin(sna, op)))
 		goto flush;
 
+	assert(op->floats_per_rect >= vertex_space(sna));
+	assert(rem <= vertex_space(sna));
 	if (want > 1 && want * op->floats_per_rect > rem)
 		want = rem / op->floats_per_rect;