Index: src/GenPoly/Box.cc
===================================================================
--- src/GenPoly/Box.cc	(revision 8d9d97467f621ca8bca5ac909252ee5506e74ea0)
+++ src/GenPoly/Box.cc	(revision d99a7168a496bfc355c644d298212bbfcfd3ef37)
@@ -556,5 +556,5 @@
 			// even when converted to strings, sort in the original order.
 			// (At least, that is the best explination I have.)
-			for ( std::pair<std::string, TypeDecl::Data> const & tyParam : exprTyVars ) {
+			for ( std::pair<const std::string, TypeDecl::Data> const & tyParam : exprTyVars ) {
 				if ( !tyParam.second.isComplete ) continue;
 				Type *concrete = env->lookup( tyParam.first );