diff --git a/protocol/src/main/scala/sbt/internal/langserver/ErrorCodes.scala b/protocol/src/main/scala/sbt/internal/langserver/ErrorCodes.scala
index 6128b25ba..4b67ee90a 100644
--- a/protocol/src/main/scala/sbt/internal/langserver/ErrorCodes.scala
+++ b/protocol/src/main/scala/sbt/internal/langserver/ErrorCodes.scala
@@ -42,6 +42,7 @@ object ErrorCodes {
 
   // The remainder of the space is available for application defined errors.
   val RequestCancelled = -32800L     // Defined by LSP
+  val UnknownError     = -33000L     // A generic error, unknown if the user or server is at fault.
 
   // format: on
 }