diff --git a/busted/core.lua b/busted/core.lua
index a00912db..6250e108 100644
--- a/busted/core.lua
+++ b/busted/core.lua
@@ -79,7 +79,7 @@ return function()
     end
 
     info.traceback = debug.traceback('', level)
-    info.message = msg
+    info.message = tostring(msg)
 
     local file = busted.getFile(element)
     return file and file.getTrace(file.name, info) or trimTrace(info)
diff --git a/busted/outputHandlers/json.lua b/busted/outputHandlers/json.lua
index 880e639d..97a07f37 100644
--- a/busted/outputHandlers/json.lua
+++ b/busted/outputHandlers/json.lua
@@ -7,13 +7,21 @@ return function(options)
   local handler = require 'busted.outputHandlers.base'()
 
   handler.suiteEnd = function()
-    io_write(json.encode({
+    local error_info = {
       pendings = handler.pendings,
       successes = handler.successes,
       failures = handler.failures,
       errors = handler.errors,
       duration = handler.getDuration()
-    }))
+    }
+    local ok, result = pcall(json.encode, error_info)
+
+    if ok then
+      io_write(result)
+    else
+      io_write("Failed to encode test results to json: " .. result)
+    end
+
     io_write("\n")
     io_flush()