diff --git a/invokeai/app/api/routers/model_manager.py b/invokeai/app/api/routers/model_manager.py
index ffb7e909e5..a0c5ad8017 100644
--- a/invokeai/app/api/routers/model_manager.py
+++ b/invokeai/app/api/routers/model_manager.py
@@ -847,24 +847,37 @@ async def set_cache_size(
     """Set the current RAM or VRAM cache size setting (in GB). ."""
     cache = ApiDependencies.invoker.services.model_manager.load.ram_cache
     app_config = get_config()
+    vram_bak, ram_bak = (app_config.vram, app_config.ram)
+
     if cache_type == CacheType.RAM:
         cache.max_cache_size = value
         app_config.ram = value
     elif cache_type == CacheType.VRAM:
         cache.max_vram_cache_size = value
         app_config.vram = value
+    else:
+        raise ValueError(f"Unexpected {cache_type=}.")
 
     if persist:
         config_path = app_config.config_file_path
-        print(f"DEBUG: config_path = {config_path}")
+        new_config_path = config_path.with_suffix(".yaml.new")
+        backup_config_path = config_path.with_suffix(".yaml.bak")
+        shutil.copy(config_path, backup_config_path)
         try:
-            shutil.copy(config_path, config_path.with_suffix(".yaml.bak"))
-            app_config.write_file(config_path)
+            app_config.write_file(new_config_path)
+            shutil.move(new_config_path, config_path)
         except Exception as e:
-            shutil.move(config_path.with_suffix(".yaml.bak"), config_path)
-            raise RuntimeError(f"Failed to write modified configuration to {config_path}: {e}") from e
+            shutil.move(backup_config_path, config_path)
+            app_config.max_vram_cache_size = vram_bak
+            app_config.max_cache_size = ram_bak
+            raise RuntimeError(f"Failed to save configuration to {config_path}: {e}") from e
 
-    return cache.max_vram_cache_size if cache_type == CacheType.VRAM else cache.max_cache_size
+    if cache_type == CacheType.VRAM:
+        return cache.max_vram_cache_size
+    elif cache_type == CacheType.RAM:
+        return cache.max_cache_size
+    else:
+        raise ValueError(f"Unexpected {cache_type=}.")
 
 
 @model_manager_router.get(