diff --git a/src/libstd/json.rs b/src/libstd/json.rs
index 2adfbca70cf..64ce2794bb4 100644
--- a/src/libstd/json.rs
+++ b/src/libstd/json.rs
@@ -65,6 +65,7 @@ fn to_str(j: json) -> str {
             });
             str::concat(["{ ", str::connect(parts, ", "), " }"])
         }
+        null { "null" }
     }
 }