Index: src/GenPoly/InstantiateGeneric.cc
===================================================================
--- src/GenPoly/InstantiateGeneric.cc	(revision 258eb5c9477f29166b1ae9152e4dfdd2443eac84)
+++ src/GenPoly/InstantiateGeneric.cc	(revision ed94eac215a2568f1137e5c48ae381748645fef2)
@@ -219,8 +219,9 @@
 		StructDecl *concDecl = instantiations.lookup( inst );
 		if ( ! concDecl ) {
+			assert( inst->get_baseParameters() && "Base struct has parameters" );
 			// set concDecl to new type, insert type declaration into statements to add
 			concDecl = new StructDecl( typeNamer.newName( inst->get_name() ) );
 			substituteMembers( inst->get_baseStruct()->get_members(),
-								inst->get_baseParameters(), inst->get_parameters(),
+								*inst->get_baseParameters(), inst->get_parameters(),
 								concDecl->get_members() );
 			addDeclaration( concDecl );
@@ -246,7 +247,8 @@
 		if ( ! concDecl ) {
 			// set concDecl to new type, insert type declaration into statements to add
+			assert( inst->get_baseParameters() && "Base union has parameters" );
 			concDecl = new UnionDecl( typeNamer.newName( inst->get_name() ) );
 			substituteMembers( inst->get_baseUnion()->get_members(),
-								inst->get_baseParameters(), inst->get_parameters(),
+								*inst->get_baseParameters(), inst->get_parameters(),
 								concDecl->get_members() );
 			addDeclaration( concDecl );