diff --git a/specification/ingest/_types/Processors.ts b/specification/ingest/_types/Processors.ts
index c5fd838e6f..d26e73547b 100644
--- a/specification/ingest/_types/Processors.ts
+++ b/specification/ingest/_types/Processors.ts
@@ -1049,7 +1049,7 @@ export class InferenceProcessor extends ProcessorBase {
    * Input fields for inference and output (destination) fields for the inference results.
    * This option is incompatible with the target_field and field_map options.
    */
-  input_output?: InputConfig[]
+  input_output?: InputConfig | InputConfig[]
 
   /**
    * If true and any of the input fields defined in input_ouput are missing