Index: src/SynTree/Expression.cc
===================================================================
--- src/SynTree/Expression.cc	(revision fbcde641e97f117504d1c8e0bee89efe2630a6e8)
+++ src/SynTree/Expression.cc	(revision eaa504332f75ac9c8ba969d09fb9b509a00a27c1)
@@ -339,5 +339,5 @@
 			return TypeSubstitution( aggInst->get_baseParameters()->begin(), aggInst->get_baseParameters()->end(), aggInst->get_parameters().begin() );
 		} else {
-			assertf( false, "makeSub expects struct or union type for aggregate" );
+			assertf( false, "makeSub expects struct or union type for aggregate, but got: %s", toString( t ).c_str() );
 		}
 	}