diff --git a/pxtarget.json b/pxtarget.json
index 5f67a3a9..69267e8b 100644
--- a/pxtarget.json
+++ b/pxtarget.json
@@ -128,15 +128,7 @@
         "aspectRatio": 1.0,
         "parts": true,
         "partsAspectRatio": 0.69,
-        "dynamicBoardDefinition": true,
-        "messageSimulators": {
-            "jacdac": {
-                "url": "https://microsoft.github.io/jacdac-docs/tools/makecode-sim?webusb=0&parentOrigin=$PARENT_ORIGIN$",
-                "localHostUrl": "http://localhost:8000/tools/makecode-sim?webusb=0&parentOrigin=$PARENT_ORIGIN$",
-                "aspectRatio": 0.89,
-                "permanent": true
-            }
-        }
+        "dynamicBoardDefinition": true
     },
     "cloud": {
         "workspace": false,
diff --git a/targetconfig.json b/targetconfig.json
index 758acdac..d167228d 100644
--- a/targetconfig.json
+++ b/targetconfig.json
@@ -23,8 +23,17 @@
       "https://microsoft.github.io/ml4f/"
     ],
     "approvedRepoLib": {
-      "microsoft/pxt-jacdac": {
-        "preferred": true
+        "microsoft/pxt-jacdac": {
+          "upgrades": [ "move:jacdac/pxt-jacdac" ],
+          "hidden": true
+        },
+        "jacdac/pxt-jacdac": {
+          "preferred": true,
+          "simx": {
+              "sha": "0cd760f1d1575b8dcd8ec8abcbb780fc10ec6937",
+              "devUrl": "https://jacdac.github.io/jacdac-docs/tools/makecode-sim/"
+          }
+        }
       },
       "microsoft/pxt-ml4f": {},
       "adafruit/pxt-crickit": {