diff --git a/lib/philomena_web/templates/image/_image_meta.html.slime b/lib/philomena_web/templates/image/_image_meta.html.slime
index 200c763a..b6cc461d 100644
--- a/lib/philomena_web/templates/image/_image_meta.html.slime
+++ b/lib/philomena_web/templates/image/_image_meta.html.slime
@@ -64,7 +64,7 @@
       = @image.image_width
       | x
       = @image.image_height
-      =<> String.upcase(@image.image_format)
+      =<> String.upcase(to_string(@image.image_format))
       - size_kb = div(@image.image_size, 1024)
       - size_mb = Float.round(size_kb / 1024.0, 2)
       span title="#{size_kb} kB"