diff --git a/vegafusion-common/Cargo.toml b/vegafusion-common/Cargo.toml
index c886d211..b49b723f 100644
--- a/vegafusion-common/Cargo.toml
+++ b/vegafusion-common/Cargo.toml
@@ -7,7 +7,7 @@ license = "BSD-3-Clause"
 
 [features]
 pyarrow = [ "pyo3", "arrow/pyarrow",]
-json = [ "serde_json", "arrow/json", "chrono",]
+json = [ "serde_json/preserve_order", "arrow/json", "chrono",]
 prettyprint = [ "arrow/prettyprint",]
 
 [dependencies]
diff --git a/vegafusion-common/src/data/json_writer.rs b/vegafusion-common/src/data/json_writer.rs
index 0372800f..75bf8201 100644
--- a/vegafusion-common/src/data/json_writer.rs
+++ b/vegafusion-common/src/data/json_writer.rs
@@ -931,7 +931,7 @@ mod tests {
 
         assert_eq!(
             String::from_utf8(buf).unwrap(),
-            r#"{"duration_sec":"PT120S","duration_msec":"PT0.120S","duration_usec":"PT0.000120S","duration_nsec":"PT0.000000120S","name":"a"}
+            r#"{"duration_sec":"PT120S","duration_msec":"PT0.12S","duration_usec":"PT0.00012S","duration_nsec":"PT0.00000012S","name":"a"}
 {"duration_sec":null,"duration_msec":null,"duration_usec":null,"duration_nsec":null,"name":"b"}
 "#
         );