diff --git a/actions/attachment_thumbnail.php b/actions/attachment_thumbnail.php
index 3e5fbf222f..f0a54883b1 100644
--- a/actions/attachment_thumbnail.php
+++ b/actions/attachment_thumbnail.php
@@ -72,9 +72,12 @@ class Attachment_thumbnailAction extends AttachmentAction
                 $filepath = $file->getPath();
                 $size = $file->size;
             }
-        } catch (InvalidFilenameException $e) {
+            // XXX PHP: Upgrade to PHP 7.1
+            // FileNotFoundException | InvalidFilenameException
+        } catch (Exception $e) {
             // We don't have a file to display
-            return;
+            $this->clientError(_('No such attachment.'), 404);
+            return false;
         }
 
         $filename = MediaFile::getDisplayName($file);
diff --git a/lib/imagefile.php b/lib/imagefile.php
index 2138a03e60..1bbadd0b24 100644
--- a/lib/imagefile.php
+++ b/lib/imagefile.php
@@ -535,6 +535,11 @@ class ImageFile extends MediaFile
             throw new ServerException('No File object attached to this ImageFile object.');
         }
 
+        // File not stored locally, can't generate a thumbnail
+        if (empty($this->fileRecord->filename)) {
+            throw new FileNotStoredLocallyException($this->fileRecord);
+        }
+
         if ($width === null) {
             $width  = common_config('thumbnail', 'width');
             $height = common_config('thumbnail', 'height');