diff --git a/packages/react-reconciler/src/ReactFiberRoot.new.js b/packages/react-reconciler/src/ReactFiberRoot.new.js
index 1b338f12e3..a010f22bb2 100644
--- a/packages/react-reconciler/src/ReactFiberRoot.new.js
+++ b/packages/react-reconciler/src/ReactFiberRoot.new.js
@@ -44,7 +44,6 @@ function FiberRootNode(containerInfo, tag, hydrate) {
   this.nextKnownPendingLevel = NoWork;
   this.lastPingedTime = NoWork;
   this.lastExpiredTime = NoWork;
-  this.mutableSourceFirstPendingUpdateTime = NoWork;
   this.mutableSourceLastPendingUpdateTime = NoWork;
 
   if (enableSchedulerTracing) {
diff --git a/packages/react-reconciler/src/ReactFiberRoot.old.js b/packages/react-reconciler/src/ReactFiberRoot.old.js
index 10e0180bf6..83ecdd79ad 100644
--- a/packages/react-reconciler/src/ReactFiberRoot.old.js
+++ b/packages/react-reconciler/src/ReactFiberRoot.old.js
@@ -44,7 +44,6 @@ function FiberRootNode(containerInfo, tag, hydrate) {
   this.nextKnownPendingLevel = NoWork;
   this.lastPingedTime = NoWork;
   this.lastExpiredTime = NoWork;
-  this.mutableSourceFirstPendingUpdateTime = NoWork;
   this.mutableSourceLastPendingUpdateTime = NoWork;
 
   if (enableSchedulerTracing) {