diff --git a/post.php b/post.php
index ebb9dc81..1685d447 100644
--- a/post.php
+++ b/post.php
@@ -1290,25 +1290,31 @@ function handle_post(Context $ctx)
 
             try {
                 $ret = Metadata\sniff_image($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['width'] = $ret[0];
-                        $file['height'] = $ret[1];
-                        $file['mime'] = $ret[2];
-                    }
-                }
-                $file['is_an_image'] = false;
-            } catch (\RuntimeException $e) {
-                $file['is_an_image'] = false;
-            }
+                $ext = Metadata\mime_to_ext($ret[2]);
 
-            if (!$file['is_an_image']) {
-                if (!\in_array($file['extension'], $config['allowed_ext_files'])) {
-                    // Should be 'invalid media' really.
-                    error($config['error']['invalidimg']);
+                // Is it some kind of supported image?
+                if (\in_array($ret[2], Metadata\SUPPORTED_IMAGE_MIME_TYPES)) {
+                    // Is it allowed?
+                    if (!\in_array($ext, $config['allowed_ext'])) {
+                        error($config['error']['invalidimg']);
+                    }
+
+                    $file['is_an_image'] = true;
+                    $file['width'] = $ret[0];
+                    $file['height'] = $ret[1];
+                    $file['mime'] = $ret[2];
+                } else {
+                    // Is it a supported file?
+                    if (!\in_array($file['extension'], $config['allowed_ext_files'])) {
+                        // Should be 'invalid media' really.
+                        error($config['error']['invalidimg']);
+                    }
+                    $file['is_an_image'] = false;
                 }
+            } catch (\RuntimeException $e) {
+                $log = $ctx->get(LogDriver::class);
+                $log->log(LogDriver::ERROR, "Error while sniffing file '{$e->getMessage()}'");
+                error($config['error']['invalidimg']);
             }
 
             // Truncate filename if it is too long