diff --git a/content/browser/web_contents/web_contents_view_mac_unittest.mm b/content/browser/web_contents/web_contents_view_mac_unittest.mm
--- a/content/browser/web_contents/web_contents_view_mac_unittest.mm
+++ b/content/browser/web_contents/web_contents_view_mac_unittest.mm
@@ -148,6 +148,45 @@ TEST_F(WebContentsViewMacTest, DragPromisedFileTo_DownloadURL) {
   EXPECT_TRUE(result);
   EXPECT_EQ(target_path, actual_path);
 }
+
+// Regression test: when a file with the requested name already exists at the
+// drop destination, CreateFileForDrop() picks <name>-1.<ext> and the download
+// is written there. DragPromisedFileTo() must return THAT path so the drop
+// target (Finder, Mail, etc.) opens the freshly downloaded file rather than
+// the pre-existing local file.
+TEST_F(WebContentsViewMacTest, DragPromisedFileTo_ReturnsCollisionAdjustedPath) {
+  base::ScopedTempDir temp_dir;
+  ASSERT_TRUE(temp_dir.CreateUniqueTempDir());
+
+  // Pre-create the collision file, simulating a pre-existing user document at
+  // the drop destination.
+  base::FilePath target_path = temp_dir.GetPath().AppendASCII("Resume.pdf");
+  ASSERT_TRUE(base::WriteFile(target_path, "PRE-EXISTING USER DOCUMENT"));
+
+  DropData drop_data;
+  drop_data.file_contents = "downloaded bytes";
+
+  base::FilePath actual_path;
+  remote_cocoa::mojom::WebContentsNSViewHost* host = view();
+  bool result = host->DragPromisedFileTo(process()->GetID(),
+                                         main_test_rfh()->GetDocumentToken(),
+                                         target_path, drop_data, &actual_path);
+  EXPECT_TRUE(result);
+
+  // CreateFileForDrop() must have chosen the -1 suffix because the original
+  // name was taken.
+  base::FilePath expected_path =
+      temp_dir.GetPath().AppendASCII("Resume-1.pdf");
+  EXPECT_TRUE(base::PathExists(expected_path))
+      << "download should have been written to the -1 suffixed file";
+
+  // BUG: line 653 of web_contents_view_mac.mm clobbers the out-param back to
+  // the original (colliding) path. Without the fix this expectation FAILS and
+  // |actual_path| == |target_path|, i.e. the path of the pre-existing file.
+  EXPECT_EQ(expected_path, actual_path);
+  EXPECT_NE(target_path, actual_path);
+}

 }  // namespace
 }  // namespace content