Index: src/main/eval.c
===================================================================
--- src/main/eval.c	(revision 50047)
+++ src/main/eval.c	(working copy)
@@ -1046,6 +1046,17 @@
     PROTECT(val = eval(val, rho));
     defineVar(sym, R_NilValue, rho);
 
+    /* deal with the S4 case, try to dispatch to as.list */
+    if( TYPEOF(val) == S4SXP ){
+    	SEXP expr ; 
+    	/* probably should use DispatchOrEval here */
+    	PROTECT( expr = lang2(install("as.list"), val ));
+    	PROTECT( ans = eval( expr, rho ) ) ;
+    	val = ans ;
+    	UNPROTECT(3); /* expr, ans and val from above*/
+    	PROTECT(val);
+    }
+    
     /* deal with the case where we are iterating over a factor
        we need to coerce to character - then iterate */