diff --git a/reginaldCog/openai/content_builder.py b/reginaldCog/openai/content_builder.py
index f4ac300..cc18a04 100644
--- a/reginaldCog/openai/content_builder.py
+++ b/reginaldCog/openai/content_builder.py
@@ -48,6 +48,10 @@ class InputImage(Content):
     image_url: str = field(default=None)
     file_id: str = field(default=None)
 
+    def __post_init__(self):
+        if self.image_url is None and self.file_id is None:
+            raise ValueError("Either 'image_url' or 'file_id' must be provided.")
+
 
 @dataclass
 class UrlCitation(Content):