diff --git a/src/filters.zig b/src/filters.zig
index b86d356..48cb09d 100644
--- a/src/filters.zig
+++ b/src/filters.zig
@@ -5,6 +5,7 @@ const std_time = std.time;
 pub const FilterError = error{
     InvalidArgument,
     OutOfMemory,
+    UnknownFilter,
 };
 
 const DictEntry = struct {