diff --git i/gcc/cp/decl.c w/gcc/cp/decl.c
index 114e8d0cb01..9428fa05258 100644
--- i/gcc/cp/decl.c
+++ w/gcc/cp/decl.c
@@ -1776,7 +1776,7 @@ duplicate_decls (tree newdecl, tree olddecl, bool hiding, bool was_hidden)
 			newdecl);
 	      inform (olddecl_loc,
 		      "previous declaration %q#D", olddecl);
-	      return NULL_TREE;
+	      return error_mark_node;
 	    }
 	  /* For function versions, params and types match, but they
 	     are not ambiguous.  */