1 files changed, 1 insertions, 1 deletions
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 5496e945e31b..65e993708a34 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -163,7 +163,7 @@ void toString(EvalState & state, Expr e,
         }
     }
 
-    else throw TypeError(format("%1% is not allowed as a derivation argument") % showType(e));
+    else throw TypeError(format("cannot convert %1% to a string") % showType(e));
     
 }