diff --git a/tools/project.py b/tools/project.py
index 727d45c..cee5583 100644
--- a/tools/project.py
+++ b/tools/project.py
@@ -1177,6 +1177,13 @@ def generate_objdiff_config(
     if build_config is None:
         return
 
+    # Load existing objdiff.json
+    existing_units = {}
+    if Path("objdiff.json").is_file():
+        with open("objdiff.json", "r", encoding="utf-8") as r:
+            existing_config = json.load(r)
+            existing_units = {unit["name"]: unit for unit in existing_config["units"]}
+
     objdiff_config: Dict[str, Any] = {
         "min_version": "2.0.0-beta.5",
         "custom_make": "ninja",
@@ -1234,15 +1241,27 @@ def generate_objdiff_config(
     ) -> None:
         obj_path, obj_name = build_obj["object"], build_obj["name"]
         base_object = Path(obj_name).with_suffix("")
+        name = str(Path(module_name) / base_object).replace(os.sep, "/")
         unit_config: Dict[str, Any] = {
-            "name": Path(module_name) / base_object,
+            "name": name,
             "target_path": obj_path,
+            "base_path": None,
+            "scratch": None,
             "metadata": {
-                "auto_generated": build_obj["autogenerated"],
+                "complete": None,
+                "reverse_fn_order": None,
+                "source_path": None,
                 "progress_categories": progress_categories,
+                "auto_generated": build_obj["autogenerated"],
             },
+            "symbol_mappings": None,
         }
 
+        # Preserve existing symbol mappings
+        existing_unit = existing_units.get(name)
+        if existing_unit is not None:
+            unit_config["symbol_mappings"] = existing_unit.get("symbol_mappings")
+
         obj = objects.get(obj_name)
         if obj is None:
             objdiff_config["units"].append(unit_config)
@@ -1352,13 +1371,21 @@ def generate_objdiff_config(
     for category in config.progress_categories:
         add_category(category.id, category.name)
 
+    def cleandict(d):
+        if isinstance(d, dict):
+            return {k: cleandict(v) for k, v in d.items() if v is not None}
+        elif isinstance(d, list):
+            return [cleandict(v) for v in d]
+        else:
+            return d
+
     # Write objdiff.json
     with open("objdiff.json", "w", encoding="utf-8") as w:
 
         def unix_path(input: Any) -> str:
             return str(input).replace(os.sep, "/") if input else ""
 
-        json.dump(objdiff_config, w, indent=4, default=unix_path)
+        json.dump(cleandict(objdiff_config), w, indent=2, default=unix_path)
 
 
 # Calculate, print and write progress to progress.json
@@ -1480,4 +1507,4 @@ def calculate_progress(config: ProjectConfig) -> None:
         add_category(category["id"], category["measures"])
 
     with open(out_path / "progress.json", "w", encoding="utf-8") as w:
-        json.dump(progress_json, w, indent=4)
+        json.dump(progress_json, w, indent=2)