--- ETL/_surface.h~	2016-11-30 04:59:46.000000000 -0600
+++ ETL/_surface.h	2017-03-07 08:08:04.027014347 -0600
@@ -190,7 +190,7 @@
 
 	value_prep_type cooker_;
 
-	void swap(const surface &x)
+	void swap(surface &x)
 	{
 		std::swap(data_,x.data_);
 		std::swap(zero_pos_,x.zero_pos_);