diff --git a/src/sna/blt.c b/src/sna/blt.c
index ac20372e..1d5cace0 100644
--- a/src/sna/blt.c
+++ b/src/sna/blt.c
@@ -50,6 +50,8 @@ memcpy_blt(const void *src, void *dst, int bpp,
 
 	assert(width && height);
 	assert(bpp >= 8);
+	assert((src_x + width) * bpp <= 8 * src_stride);
+	assert((dst_x + width) * bpp <= 8 * dst_stride);
 
 	DBG(("%s: src=(%d, %d), dst=(%d, %d), size=%dx%d, pitch=%d/%d\n",
 	     __FUNCTION__, src_x, src_y, dst_x, dst_y, width, height, src_stride, dst_stride));
diff --git a/src/sna/sna_accel.c b/src/sna/sna_accel.c
index a6353723..aa12ec57 100644
--- a/src/sna/sna_accel.c
+++ b/src/sna/sna_accel.c
@@ -1053,6 +1053,16 @@ sna_put_image_blt(DrawablePtr drawable, GCPtr gc, RegionPtr region,
 	box = REGION_RECTS(region);
 	n = REGION_NUM_RECTS(region);
 	do {
+		assert(box->x1 >= 0);
+		assert(box->y1 >= 0);
+		assert(box->x2 <= pixmap->drawable.width);
+		assert(box->y2 <= pixmap->drawable.height);
+
+		assert(box->x1 - x >= 0);
+		assert(box->y1 - y >= 0);
+		assert(box->x2 - x <= w);
+		assert(box->y2 - y <= h);
+
 		memcpy_blt(bits, dst_bits,
 			   pixmap->drawable.bitsPerPixel,
 			   stride, dst_stride,