diff --git a/src/dj.c b/src/dj.c
index 2be2ecb..4dc4842 100644
--- a/src/dj.c
+++ b/src/dj.c
@@ -93,7 +93,9 @@ Io_write(struct Io *io){
 	assert(io->bufuse > 0);
 	assert(io->bufuse <= io->bs);
 
-	if((t = write(io->fd, io->buf, io->bufuse)) > 0)
+	if((t = write(io->fd, io->buf, io->bufuse)) < 0)
+		t = 0;
+	else if(t > 0)
 		memmove(io->buf, &(io->buf)[t], (io->bufuse -= t));
 
 	io->bytes += t;
@@ -268,6 +270,7 @@ int main(int argc, char *argv[]){
 			t = io[0].bufuse;
 			if(Io_read(&io[0])->bufuse == t && !noerror)
 				Io_read(&io[0]); /* second chance */
+			assert(io[0].bufuse >= t);
 			if(io[0].bufuse == t) /* that's all she wrote */
 				break;
 
@@ -321,6 +324,7 @@ int main(int argc, char *argv[]){
 			t = io[1].bufuse;
 			if(Io_write(&io[1])->bufuse == t && !noerror)
 				Io_write(&io[1]); /* second chance */
+			assert(io[1].bufuse <= t);
 			if(io[1].bufuse == t){ /* no more love */
 				count = 1;
 				break;