diff --git a/src/fix-ng/primops.cc b/src/fix-ng/primops.cc
index df5747edd..fb923ed46 100644
--- a/src/fix-ng/primops.cc
+++ b/src/fix-ng/primops.cc
@@ -114,6 +114,8 @@ static string processBinding(EvalState & state, Expr e, NixExpr & ne)
         }
 	return s;
     }
+
+    if (ATmatch(e, "Null")) return "";
     
     throw badTerm("invalid derivation binding", e);
 }