diff --git a/commands/handler.go b/commands/handler.go
index 8aadb44..678883d 100644
--- a/commands/handler.go
+++ b/commands/handler.go
@@ -69,7 +69,15 @@
 	}
 
 	for k, v := range fields {
-		dmsg.TrySetFieldByName(k, v)
+		// _json is a special field name that indicates we should unmarshal json data
+		if k == "_json" {
+			err = dmsg.UnmarshalMergeJSON(v.([]byte))
+			if err != nil {
+				return err
+			}
+		} else {
+			dmsg.SetFieldByName(k, v)
+		}
 	}
 	delete(h.Fields, dmsg.XXX_MessageName())