diff --git a/HMCL/src/main/java/org/jackhuang/hmcl/ui/instances/ClientSyncProgress.java b/HMCL/src/main/java/org/jackhuang/hmcl/ui/instances/ClientSyncProgress.java
index 156ee2b5b2..635587faf8 100644
--- a/HMCL/src/main/java/org/jackhuang/hmcl/ui/instances/ClientSyncProgress.java
+++ b/HMCL/src/main/java/org/jackhuang/hmcl/ui/instances/ClientSyncProgress.java
@@ -4,6 +4,7 @@ package org.jackhuang.hmcl.ui.instances;
 
 import javafx.beans.property.*;
 import org.jackhuang.hmcl.task.FetchTask;
+import org.jackhuang.hmcl.task.FileDownloadTask;
 import org.jackhuang.hmcl.task.Task;
 import org.jackhuang.hmcl.task.TaskExecutor;
 import org.jackhuang.hmcl.task.TaskListener;
@@ -19,8 +20,7 @@ import java.util.function.Consumer;
 ///
 /// The model is only a view of the task executor started by [Instances#ensureClientAndJoin(ClientSyncProgress)]:
 /// it never changes what is downloaded. All properties must be read and written on the JavaFX thread.
-/// Overall percentage is estimated from the number of finished tasks, so it never moves backwards but
-/// may advance unevenly while new tasks are discovered.
+/// Overall percentage is estimated from finished file downloads against the total announced by the sync task, and stays indeterminate until that total is known.
 @NotNullByDefault
 public final class ClientSyncProgress {
 
@@ -53,8 +53,12 @@ public final class ClientSyncProgress {
 
     private @Nullable TaskExecutor executor;
     private long downloadedBytes;
-    private int seenTasks;
-    private int finishedTasks;
+    /// Total number of downloads announced by tasks so far.
+    private int expectedFiles;
+    /// Number of finished file downloads.
+    private int finishedFiles;
+    /// Tasks whose `total` has already been added to [#expectedFiles].
+    private final java.util.Set<Task<?>> announcedTasks = java.util.Collections.newSetFromMap(new java.util.IdentityHashMap<>());
     private boolean cancelled;
 
     /// Keeps the weakly registered speed listener alive.
@@ -101,8 +105,9 @@ public final class ClientSyncProgress {
         executor = null;
         cancelled = false;
         downloadedBytes = 0;
-        seenTasks = 0;
-        finishedTasks = 0;
+        expectedFiles = 0;
+        finishedFiles = 0;
+        announcedTasks.clear();
         progress.set(-1);
         detail.set("");
         error.set("");
@@ -149,6 +154,15 @@ public final class ClientSyncProgress {
         return cancelled;
     }
 
+    /// Recomputes the fraction from finished downloads; stays indeterminate until a total is known.
+    private void refreshProgress(TaskExecutor current) {
+        if (executor != current || expectedFiles <= 0)
+            return;
+        double value = Math.min(0.99, (double) finishedFiles / expectedFiles);
+        if (value > progress.get())
+            progress.set(value);
+    }
+
     /// Submits `task` to the serial task queue and mirrors its task count into the progress.
     ///
     /// @param task the task to run
@@ -156,21 +170,28 @@ public final class ClientSyncProgress {
         TaskExecutor taskExecutor = task.executor();
         executor = taskExecutor;
         taskExecutor.addTaskListener(new TaskListener() {
+            /// Tasks announce how many downloads they will start through the `total` property
+            /// (set once the file list is known), so the denominator never grows with discovered tasks.
             @Override
-            public void onReady(Task<?> ready) {
-                FXUtils.runInFX(() -> seenTasks++);
+            public void onPropertiesUpdate(Task<?> updated) {
+                Object total = updated.getProperties().get("total");
+                if (total instanceof Integer count && count > 0) {
+                    FXUtils.runInFX(() -> {
+                        if (announcedTasks.add(updated))
+                            expectedFiles += count;
+                        refreshProgress(taskExecutor);
+                    });
+                }
             }
 
             @Override
             public void onFinished(Task<?> finishedTask) {
-                FXUtils.runInFX(() -> {
-                    finishedTasks++;
-                    if (executor != taskExecutor || seenTasks <= 0)
-                        return;
-                    double value = Math.min(0.99, (double) finishedTasks / seenTasks);
-                    if (value > progress.get())
-                        progress.set(value);
-                });
+                if (finishedTask instanceof FileDownloadTask) {
+                    FXUtils.runInFX(() -> {
+                        finishedFiles++;
+                        refreshProgress(taskExecutor);
+                    });
+                }
             }
         });
         TaskManager.getInstance().submit(taskExecutor, null);