diff --git a/engine/baml-lib/jsonish/src/tests/test_unions.rs b/engine/baml-lib/jsonish/src/tests/test_unions.rs
index 5b93ca6b4..fc6d9dc79 100644
--- a/engine/baml-lib/jsonish/src/tests/test_unions.rs
+++ b/engine/baml-lib/jsonish/src/tests/test_unions.rs
@@ -70,3 +70,176 @@ test_deserializer!(
     "data": null
   }
 );
+
+const MAP_VS_CLASS: &str = r###"
+class Page {
+    object string @description("Always page")
+    // children (Bookmark | Breadcrumb | BulletedListItem | Callout | Code | ColumnList | Divider | Embed | Equation | File | Heading1 | Heading2 | Heading3 | ImageFile | NumberedListItem | Paragraph | PDF | Quote | Table | TableOfContents | ToDo | Toggle | Video)[] @description("Some blocks of the page")
+    children (Breadcrumb | ColumnList)[] @description("Some blocks of the page")
+}
+
+// ------------ Breadcrumb ----------------
+class Breadcrumb {
+  type string @description("Always breadcrumb")
+  breadcrumb map<string, string> @description("Always empty map")
+}
+
+/// ------------ Column List ----------------
+class ColumnList {
+  type string @description("Always column_list")
+  column_list ColumnListBody @description("Column list block with columns")
+}
+
+class ColumnListBody {
+  children Column[] @description("The columns in the column list. Max length is 5")
+}
+
+class Column {
+  type string @description("Always column")
+  column ColumnBody @description("Always empty map for columns")
+}
+
+class ColumnBody {
+  // children (Bookmark | Breadcrumb | BulletedListItem | Callout | Code | Divider | Embed | Equation | File | Heading1 | Heading2 | Heading3 | ImageFile | NumberedListItem | Paragraph | PDF | Quote | Table | TableOfContents | ToDo | Toggle | Video)[] @description("Content of the column. Can contain any block type. Min length is 1")
+  children (Breadcrumb | Paragraph)[] 
+}
+
+/// ------------ Other blocks ----------------
+/// 
+class Paragraph {
+  type string @description("Always paragraph")
+  paragraph string
+}
+"###;
+
+test_deserializer!(
+  prefer_class_to_map,
+  MAP_VS_CLASS,
+  r#"```json
+  {
+    "object": "page",
+    "children": [
+      {
+        "type": "column_list",
+        "column_list": {
+          "children": [
+            {
+              "type": "column",
+              "column": {
+                "children": [
+                  {
+                    "untyped": "lorem ipsum",
+                  },
+                  {
+                    "untyped": "lorem ipsum",
+                  },
+                  {
+                    "untyped": "lorem ipsum",
+                  },
+                  {
+                    "type": "paragraph",
+                    "paragraph":  "J.R.R. Tolkien",
+                  },
+                  {
+                    "type": "to_do",
+                    "to_do": {
+                    "untyped": "dolor sit amet",
+                      "rich_text": [
+                        {
+                          "type": "text",
+                          "text": {
+                            "content": "Read again"
+                          }
+                        }
+                      ],
+                      "checked": false
+                    }
+                  }
+                ]
+              }
+            }
+          ]
+        }
+      }
+    ]
+  }
+  ```"#,
+  FieldType::class("Page"),
+  {
+    "children": [
+      {
+        "type": "column_list",
+        "column_list": {
+          "children": [
+            {
+              "type": "column",
+              "column": {
+                "children": [
+                  {
+                    "type": "paragraph",
+                    "paragraph":  "J.R.R. Tolkien",
+                  },
+                ]
+              }
+            }
+          ]
+        }
+      }
+    ]
+  }
+);
+
+test_deserializer!(
+  array_of_union_should_drop_unknown,
+  MAP_VS_CLASS,
+  r#"```json
+  {
+    "children": [
+      {
+        "untyped": "lorem ipsum",
+      },
+      {
+        "untyped": "lorem ipsum",
+      },
+      {
+        "untyped": "lorem ipsum",
+      },
+      {
+        "untyped": "lorem ipsum",
+      },
+      {
+        "type": "paragraph",
+        "paragraph":  "J.R.R. Tolkien",
+      },
+      {
+        "type": "to_do",
+        "to_do": {
+        "untyped": "dolor sit amet",
+          "rich_text": [
+            {
+              "type": "text",
+              "text": {
+                "content": "Read again"
+              }
+            }
+          ],
+          "checked": false
+        }
+      }
+    ]
+  }
+  ```"#,
+  FieldType::class("ColumnBody"),
+  {
+    "children": [
+      {
+        "type": "paragraph",
+        "paragraph":  "J.R.R. Tolkien",
+      },
+      {
+        "type": "to_do",
+        "breadcrumb": {},
+      }
+    ]
+  }
+);