diff --git a/packages/react-devtools-shared/src/backend/renderer.js b/packages/react-devtools-shared/src/backend/renderer.js
index e6943396874..506afcedcf3 100644
--- a/packages/react-devtools-shared/src/backend/renderer.js
+++ b/packages/react-devtools-shared/src/backend/renderer.js
@@ -2345,6 +2345,18 @@ export function attach(
       const prevFallbackChildSet = prevFiberChild
         ? prevFiberChild.sibling
         : null;
+
+      if (prevFallbackChildSet == null && nextFallbackChildSet != null) {
+        mountFiberRecursively(
+          nextFallbackChildSet,
+          shouldIncludeInTree ? nextFiber : parentFiber,
+          true,
+          traceNearestHostComponentUpdate,
+        );
+
+        shouldResetChildren = true;
+      }
+
       if (
         nextFallbackChildSet != null &&
         prevFallbackChildSet != null &&
diff --git a/packages/react-devtools-shared/src/hook.js b/packages/react-devtools-shared/src/hook.js
index 39af7daa374..4df992e23ea 100644
--- a/packages/react-devtools-shared/src/hook.js
+++ b/packages/react-devtools-shared/src/hook.js
@@ -320,7 +320,7 @@ export function installHook(target: any): DevToolsHook | null {
 
   let uidCounter = 0;
 
-  function inject(renderer: ReactRenderer) {
+  function inject(renderer: ReactRenderer): number {
     const id = ++uidCounter;
     renderers.set(id, renderer);