Index: src/InitTweak/InitTweak.cc
===================================================================
--- src/InitTweak/InitTweak.cc	(revision b1e63ac54a1b3b3705d130858c9772e8b84c867f)
+++ src/InitTweak/InitTweak.cc	(revision a61ad31375e748db470d1432e85336461752723c)
@@ -380,5 +380,5 @@
 		template<typename CallExpr>
 		Expression *& callArg( CallExpr * callExpr, unsigned int pos ) {
-			if ( pos >= callExpr->get_args().size() ) assertf( false, "asking for argument that doesn't exist. Return NULL/throw exception?" );
+			if ( pos >= callExpr->get_args().size() ) assertf( false, "getCallArg for argument that doesn't exist: (%u); %s.", pos, toString( callExpr ).c_str() );
 			for ( Expression *& arg : callExpr->get_args() ) {
 				if ( pos == 0 ) return arg;