diff --git a/.github/scripts/upl_ytdlp_checksum_patch.py b/.github/scripts/upl_ytdlp_checksum_patch.py
new file mode 100644
index 00000000000..e05b322a3d4
--- /dev/null
+++ b/.github/scripts/upl_ytdlp_checksum_patch.py
@@ -0,0 +1,48 @@
+from pathlib import Path
+
+service_path = Path("src/ui/Logic/Download/YtDlpDownloadService.cs")
+service = service_path.read_text(encoding="utf-8-sig")
+old = '''        var assetName = Path.GetFileName(filePath);
+        if (!KnownSha256.TryGetValue(version, out var byAsset) ||
+'''
+new = '''        var assetName = Path.GetFileName(filePath);
+        if (assetName.EndsWith(".part", StringComparison.Ordinal))
+        {
+            assetName = assetName[..^".part".Length];
+        }
+
+        if (!KnownSha256.TryGetValue(version, out var byAsset) ||
+'''
+assert service.count(old) == 1, service.count(old)
+service = service.replace(old, new)
+service_path.write_text(service, encoding="utf-8")
+
+test_path = Path("tests/UI/Logic/Download/YtDlpDownloadServiceTests.cs")
+test = test_path.read_text(encoding="utf-8-sig")
+anchor = '''    [Fact]
+    public async Task VerifyChecksumAsync_UnknownAsset_IsNoOp_AndKeepsFile()
+'''
+regression = '''    [Fact]
+    public async Task VerifyChecksumAsync_PartFile_Mismatch_ThrowsAndDeletesFile()
+    {
+        var dir = Path.Combine(Path.GetTempPath(), "VerifyPartMismatch_" + Guid.NewGuid().ToString("N"));
+        Directory.CreateDirectory(dir);
+        var path = Path.Combine(dir, "yt-dlp.exe.part");
+        await File.WriteAllTextAsync(path, "this is not really yt-dlp", TestContext.Current.CancellationToken);
+        try
+        {
+            await Assert.ThrowsAsync<InvalidOperationException>(() =>
+                YtDlpDownloadService.VerifyChecksumAsync(path, YtDlpDownloadService.CurrentVersion, TestContext.Current.CancellationToken));
+
+            Assert.False(File.Exists(path), "A downloaded .part binary that fails verification must be deleted.");
+        }
+        finally
+        {
+            Directory.Delete(dir, recursive: true);
+        }
+    }
+
+'''
+assert test.count(anchor) == 1, test.count(anchor)
+test = test.replace(anchor, regression + anchor)
+test_path.write_text(test, encoding="utf-8")
diff --git a/.github/workflows/upl-ytdlp-checksum-regression.yml b/.github/workflows/upl-ytdlp-checksum-regression.yml
new file mode 100644
index 00000000000..2aad6e7d475
--- /dev/null
+++ b/.github/workflows/upl-ytdlp-checksum-regression.yml
@@ -0,0 +1,47 @@
+name: UPL yt-dlp checksum regression
+
+on:
+  push:
+    branches:
+      - upl/fix-ytdlp-checksum-work
+
+permissions:
+  contents: write
+
+jobs:
+  patch-and-test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v5
+        with:
+          ref: fix/ytdlp-part-checksum-current
+          fetch-depth: 0
+
+      - name: Apply checksum fix and regression
+        run: |
+          git fetch origin upl/fix-ytdlp-checksum-work:refs/remotes/origin/upl/fix-ytdlp-checksum-work
+          git show refs/remotes/origin/upl/fix-ytdlp-checksum-work:.github/scripts/upl_ytdlp_checksum_patch.py > "$RUNNER_TEMP/upl_ytdlp_checksum_patch.py"
+          python "$RUNNER_TEMP/upl_ytdlp_checksum_patch.py"
+          expected=$'src/ui/Logic/Download/YtDlpDownloadService.cs\ntests/UI/Logic/Download/YtDlpDownloadServiceTests.cs'
+          actual="$(git diff --name-only HEAD | sort)"
+          test "$actual" = "$expected" || { echo "Unexpected changed files:"; printf '%s\n' "$actual"; exit 1; }
+          git diff --check HEAD
+
+      - name: Setup .NET
+        uses: actions/setup-dotnet@v5
+        with:
+          dotnet-version: '10.0.x'
+
+      - name: Targeted regression tests
+        run: dotnet test tests/UI/UITests.csproj --filter YtDlpDownloadServiceTests
+
+      - name: Full solution tests
+        run: dotnet test SubtitleEdit.sln
+
+      - name: Commit verified patch
+        run: |
+          git config user.name 'BlackSpirits'
+          git config user.email 'blackspirits@gmail.com'
+          git add src/ui/Logic/Download/YtDlpDownloadService.cs tests/UI/Logic/Download/YtDlpDownloadServiceTests.cs
+          git commit -m 'Verify yt-dlp temporary downloads before install'
+          git push origin HEAD:fix/ytdlp-part-checksum-current
diff --git a/src/ui/Logic/Download/YtDlpDownloadService.cs b/src/ui/Logic/Download/YtDlpDownloadService.cs
index 1b3e9c4043e..43a8b01524d 100644
--- a/src/ui/Logic/Download/YtDlpDownloadService.cs
+++ b/src/ui/Logic/Download/YtDlpDownloadService.cs
@@ -197,6 +197,11 @@ public async Task DownloadYtDlp(IProgress<float>? progress, CancellationToken ca
     internal static async Task VerifyChecksumAsync(string filePath, string version, CancellationToken cancellationToken)
     {
         var assetName = Path.GetFileName(filePath);
+        if (assetName.EndsWith(".part", StringComparison.Ordinal))
+        {
+            assetName = assetName[..^".part".Length];
+        }
+
         if (!KnownSha256.TryGetValue(version, out var byAsset) ||
             !byAsset.TryGetValue(assetName, out var expected))
         {
diff --git a/tests/UI/Logic/Download/YtDlpDownloadServiceTests.cs b/tests/UI/Logic/Download/YtDlpDownloadServiceTests.cs
index c1781ba55d8..4431ba57c16 100644
--- a/tests/UI/Logic/Download/YtDlpDownloadServiceTests.cs
+++ b/tests/UI/Logic/Download/YtDlpDownloadServiceTests.cs
@@ -162,6 +162,26 @@ await Assert.ThrowsAsync<InvalidOperationException>(() =>
         }
     }
 
+    [Fact]
+    public async Task VerifyChecksumAsync_PartFile_Mismatch_ThrowsAndDeletesFile()
+    {
+        var dir = Path.Combine(Path.GetTempPath(), "VerifyPartMismatch_" + Guid.NewGuid().ToString("N"));
+        Directory.CreateDirectory(dir);
+        var path = Path.Combine(dir, "yt-dlp.exe.part");
+        await File.WriteAllTextAsync(path, "this is not really yt-dlp", TestContext.Current.CancellationToken);
+        try
+        {
+            await Assert.ThrowsAsync<InvalidOperationException>(() =>
+                YtDlpDownloadService.VerifyChecksumAsync(path, YtDlpDownloadService.CurrentVersion, TestContext.Current.CancellationToken));
+
+            Assert.False(File.Exists(path), "A downloaded .part binary that fails verification must be deleted.");
+        }
+        finally
+        {
+            Directory.Delete(dir, recursive: true);
+        }
+    }
+
     [Fact]
     public async Task VerifyChecksumAsync_UnknownAsset_IsNoOp_AndKeepsFile()
     {