diff --git a/ext/image/main.php b/ext/image/main.php
index d991a674..a43ffcf7 100644
--- a/ext/image/main.php
+++ b/ext/image/main.php
@@ -433,7 +433,8 @@ class ImageIO extends Extension {
 		}
 		if(!empty($image->source)) {
 			if(!preg_match("#^(https?|ftp)://#", $image->source)) {
-				throw new ImageReplaceException("Image's source isn't a valid URL");
+				$h_url = html_escape($image->source);
+				throw new ImageReplaceException("Image's source isn't a valid URL ($h_url)");
 			}
 		}