diff --git a/core/extension.class.php b/core/extension.class.php
index a1175341..0b4c767b 100644
--- a/core/extension.class.php
+++ b/core/extension.class.php
@@ -197,6 +197,9 @@ abstract class DataHandlerExtension extends Extension {
 				}
 			}
 		}
+		else{
+			throw new UploadException("Unsupported extension or file isn't an image");
+		}
 	}
 
 	public function onThumbnailGeneration(ThumbnailGenerationEvent $event) {