diff --git a/README.md b/README.md
index acfabe9..1cdec3c 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,6 @@
 ljkiwi - Free LuaJIT FFI kiwi (Cassowary derived) constraint solver.
 
-[![CI](https://github.com/jkl1337/ljkiwi/actions/workflows/ci.yml/badge.svg)](https://github.com/jkl1337/ljkiwi/actions/workflows/ci.yml)
+[![CI](https://github.com/jkl1337/ljkiwi/actions/workflows/busted.yml/badge.svg)](https://github.com/jkl1337/ljkiwi/actions/workflows/busted.yml)
 [![Coverage Status](https://coveralls.io/repos/github/jkl1337/ljkiwi/badge.svg?branch=master)](https://coveralls.io/github/jkl1337/ljkiwi?branch=master)
 [![luarocks](https://img.shields.io/luarocks/v/jkl/ljkiwi)](https://luarocks.org/modules/jkl/ljkiwi)
 
diff --git a/kiwi.lua b/kiwi.lua
index 9a60ab0..f116ba7 100644
--- a/kiwi.lua
+++ b/kiwi.lua
@@ -871,7 +871,8 @@ do
    function kiwi.error_mask(kinds, invert)
       local mask = 0
       for _, k in ipairs(kinds) do
-         mask = bor(mask, lshift(1, kiwi.ErrKind(k)))
+         -- must use tonumber only for LuaJIT 2.0 compatibility
+         mask = bor(mask, lshift(1, tonumber(kiwi.ErrKind(k)) --[[@as integer]]))
       end
       return invert and bit.bnot(mask) or mask
    end
@@ -940,8 +941,9 @@ do
          end
          local errdata = new_error(kind, message, solver, item)
          local error_mask = solver and solver.error_mask_ or 0
+         -- tonumber only required for LuaJIT 2.0 compatibility
          return item,
-            band(error_mask, lshift(1, kind --[[@as integer]])) == 0 and error(errdata)
+            band(error_mask, lshift(1, tonumber(kind) --[[@as integer]])) == 0 and error(errdata)
                or errdata
       end
       return item