Index: src/AST/TypeEnvironment.cpp
===================================================================
--- src/AST/TypeEnvironment.cpp	(revision 93f74c0f041d552f34efb8041fc88182fa70b0c6)
+++ src/AST/TypeEnvironment.cpp	(revision 1f68d5d103ce802b81fc6891deddf85f956a0455)
@@ -115,5 +115,5 @@
 
 void TypeEnvironment::add( const TypeSubstitution & sub ) {
-	for ( const auto p : sub ) {
+	for ( const auto & p : sub ) {
 		add( EqvClass{ p.first, p.second } );
 	}