diff --git a/lua/java-core/utils/async.lua b/lua/java-core/utils/async.lua
index 5d67fff..8649de7 100644
--- a/lua/java-core/utils/async.lua
+++ b/lua/java-core/utils/async.lua
@@ -38,7 +38,7 @@ local function async(func)
 					return
 				end
 
-				error('unhandled error ' .. thunk)
+				error('unhandled error ' .. tostring(thunk))
 			end
 
 			assert(ok, thunk)