diff --git a/shard.yml b/shard.yml
index b853afe..3d3734e 100644
--- a/shard.yml
+++ b/shard.yml
@@ -13,6 +13,6 @@ dependencies:
     github: kemalcr/kemal
     version: ~> 0.26.1
 
-crystal: 0.33.0
+crystal: 0.34.0
 
 license: AGPLv3
diff --git a/src/instances.cr b/src/instances.cr
index 80d77e6..d3d1a61 100644
--- a/src/instances.cr
+++ b/src/instances.cr
@@ -156,6 +156,8 @@ def sort_instances(instances, sort_by)
         compare = first <=> sort.call(b[0], b[1]).as(Float64)
       when String
         compare = first <=> sort.call(b[0], b[1]).as(String)
+      else
+        raise "Invalid proc"
       end
       break if compare != 0
     end