diff --git a/post.php b/post.php
index 328aedc1..ebb9dc81 100644
--- a/post.php
+++ b/post.php
@@ -1289,12 +1289,14 @@ function handle_post(Context $ctx)
             }
 
             try {
-                $mime = Metadata\sniff_image($file['tmp_name'])[3];
-                if (\in_array($mime, Metadata\SUPPORTED_IMAGE_MIME_TYPES)) {
-                    $ext = Metadata\mime_to_ext($mime);
+                $ret = Metadata\sniff_image($file['tmp_name']);
+                if (\in_array($ret[2], Metadata\SUPPORTED_IMAGE_MIME_TYPES)) {
+                    $ext = Metadata\mime_to_ext($ret[2]);
                     $file['is_an_image'] = !\in_array($ext, $config['allowed_ext_files']);
                     if ($file['is_an_image']) {
-                        $file['mime'] = $mime;
+                        $file['width'] = $ret[0];
+                        $file['height'] = $ret[1];
+                        $file['mime'] = $ret[2];
                     }
                 }
                 $file['is_an_image'] = false;
@@ -1302,6 +1304,13 @@ function handle_post(Context $ctx)
                 $file['is_an_image'] = false;
             }
 
+            if (!$file['is_an_image']) {
+                if (!\in_array($file['extension'], $config['allowed_ext_files'])) {
+                    // Should be 'invalid media' really.
+                    error($config['error']['invalidimg']);
+                }
+            }
+
             // Truncate filename if it is too long
             $file['filename'] = mb_substr($file['filename'], 0, $config['max_filename_len']);