$OpenBSD: patch-src_modelmeasure_cpp,v 1.1 2017/04/30 08:56:45 espie Exp $
--- src/modelmeasure.cpp.orig
+++ src/modelmeasure.cpp
@@ -42,6 +42,7 @@ Foundation, Inc., 59 Temple Place, Suite 330, Boston, 
 #include "primitives.h"
 
 using namespace std;
+using dd::mutex;
 
 /*
   - measure cross section (graphical)
