diff --git a/src/feature_collection.rs b/src/feature_collection.rs
index 6a9fc33..5bd28ca 100644
--- a/src/feature_collection.rs
+++ b/src/feature_collection.rs
@@ -71,6 +71,7 @@ pub struct FeatureCollection {
     /// Foreign Members
     ///
     /// [GeoJSON Format Specification § 6](https://tools.ietf.org/html/rfc7946#section-6)
+    #[serde(flatten)]
     pub foreign_members: Option<JsonObject>,
 }
 
diff --git a/tests/roundtrip.rs b/tests/roundtrip.rs
index 12eb7ec..c4a7687 100644
--- a/tests/roundtrip.rs
+++ b/tests/roundtrip.rs
@@ -63,6 +63,12 @@ mod roundtrip_tests {
         let original_json: serde_json::Value = serde_json::from_str(&file_contents).unwrap();
         let roundtrip_json: serde_json::Value = serde_json::from_str(&geojson_string).unwrap();
 
-        assert_eq!(original_json, roundtrip_json)
+        assert_eq!(
+            original_json,
+            roundtrip_json,
+            "inconsistent round trip: {file_path}. \n\n original: {} \n\n roundtrip: {}",
+            serde_json::to_string_pretty(&original_json).unwrap(),
+            serde_json::to_string_pretty(&roundtrip_json).unwrap()
+        );
     }
 }