diff --git a/libvips/foreign/radiance.c b/libvips/foreign/radiance.c
index 57fbae83..6903221b 100644
--- a/libvips/foreign/radiance.c
+++ b/libvips/foreign/radiance.c
@@ -1295,11 +1295,16 @@ static int
 vips2rad_put_data_block( VipsRegion *region, VipsRect *area, void *a )
 {
 	Write *write = (Write *) a;
-	size_t size;
-	unsigned char *buffer = vips_dbuf_get_write( &write->dbuf, &size );
 
+	size_t size;
+	unsigned char *buffer;
 	int i;
 
+	/* You have to seek back after a write.
+	 */
+	buffer = vips_dbuf_get_write( &write->dbuf, &size );
+	vips_dbuf_seek( &write->dbuf, 0, SEEK_SET ); 
+
 	g_assert( size >= MAX_LINE ); 
 
 	for( i = 0; i < area->height; i++ ) {