diff --git a/ui/accessibility/platform/ax_platform_node_win.cc b/ui/accessibility/platform/ax_platform_node_win.cc
index 85a012a849e71c..f13a6cc57db447 100644
--- a/ui/accessibility/platform/ax_platform_node_win.cc
+++ b/ui/accessibility/platform/ax_platform_node_win.cc
@@ -367,6 +367,11 @@ AXPlatformNodeWin::~AXPlatformNodeWin() {
     g_unique_id_map.Get().erase(unique_id_);
 }
 
+// static
+size_t AXPlatformNodeWin::GetInstanceCountForTesting() {
+  return g_unique_id_map.Get().size();
+}
+
 const base::char16 AXPlatformNodeWin::kEmbeddedCharacter = L'\xfffc';
 
 void AXPlatformNodeWin::CalculateRelationships() {
diff --git a/ui/accessibility/platform/ax_platform_node_win.h b/ui/accessibility/platform/ax_platform_node_win.h
index 9bfdd15a196c6d..a5af54561a62f8 100644
--- a/ui/accessibility/platform/ax_platform_node_win.h
+++ b/ui/accessibility/platform/ax_platform_node_win.h
@@ -292,6 +292,9 @@ class AX_EXPORT __declspec(uuid("26f5641a-246d-457b-a96d-07f3fae6acf2"))
 
   ~AXPlatformNodeWin() override;
 
+  // Return the number of instances of AXPlatformNodeWin, for leak testing.
+  static size_t GetInstanceCountForTesting();
+
   // Represents a non-static text node in IAccessibleHypertext. This character
   // is embedded in the response to IAccessibleText::get_text, indicating the
   // position where a non-static text child object appears.
diff --git a/ui/accessibility/platform/ax_platform_node_win_unittest.cc b/ui/accessibility/platform/ax_platform_node_win_unittest.cc
index eef013f827cae5..bbaf4a46b55217 100644
--- a/ui/accessibility/platform/ax_platform_node_win_unittest.cc
+++ b/ui/accessibility/platform/ax_platform_node_win_unittest.cc
@@ -44,6 +44,12 @@ class AXPlatformNodeWinTest : public ui::AXPlatformNodeTest {
     win::CreateATLModuleIfNeeded();
   }
 
+  void TearDown() override {
+    // Destroy the tree and make sure we're not leaking any objects.
+    tree_.reset(nullptr);
+    ASSERT_EQ(0U, AXPlatformNodeWin::GetInstanceCountForTesting());
+  }
+
  protected:
   void BuildRelationships(ComPtr<IAccessible2> accessible) {
     CHECK(accessible);