diff --git a/ui/media/main.js b/ui/media/main.js
index cdf76066..bc7c4439 100644
--- a/ui/media/main.js
+++ b/ui/media/main.js
@@ -519,7 +519,7 @@ async function doMakeImage(task) {
                 stepUpdate = JSON.parse(finalJSON)
                 finalJSON = jsonStr
             } catch (e) {
-                if (e instanceof SyntaxError) {
+                if (e instanceof SyntaxError && !readComplete) {
                     finalJSON += jsonStr
                 } else {
                     throw e