diff --git a/build/busted b/build/busted
index 4c5299de2..a24dd4cae 100755
--- a/build/busted
+++ b/build/busted
@@ -1,3 +1,16 @@
 #!/usr/bin/env resty
 
+local ffi = require("ffi")
+
+-- without this we get errors such as "attempt to redefine XXX"
+local old_cdef = ffi.cdef
+local exists = {}
+ffi.cdef = function(def)
+  if exists[def] then
+    return
+  end
+  exists[def] = true
+  return old_cdef(def)
+end
+
 require "busted.runner"({ standalone = false })