diff --git a/src/System.Windows.Forms/System/Windows/Forms/Controls/ListBoxes/ListBox.IntegerCollection.cs b/src/System.Windows.Forms/System/Windows/Forms/Controls/ListBoxes/ListBox.IntegerCollection.cs
index 421247d5b70..932bc047604 100644
--- a/src/System.Windows.Forms/System/Windows/Forms/Controls/ListBoxes/ListBox.IntegerCollection.cs
+++ b/src/System.Windows.Forms/System/Windows/Forms/Controls/ListBoxes/ListBox.IntegerCollection.cs
@@ -43,7 +43,7 @@ bool ICollection.IsSynchronized
         {
             get
             {
-                return true;
+                return false;
             }
         }
 
diff --git a/src/System.Windows.Forms/System/Windows/Forms/Controls/ListBoxes/ListBox.SelectedIndexCollection.cs b/src/System.Windows.Forms/System/Windows/Forms/Controls/ListBoxes/ListBox.SelectedIndexCollection.cs
index 31b0100cfba..f8c5aeea6e3 100644
--- a/src/System.Windows.Forms/System/Windows/Forms/Controls/ListBoxes/ListBox.SelectedIndexCollection.cs
+++ b/src/System.Windows.Forms/System/Windows/Forms/Controls/ListBoxes/ListBox.SelectedIndexCollection.cs
@@ -41,7 +41,7 @@ bool ICollection.IsSynchronized
         {
             get
             {
-                return true;
+                return false;
             }
         }
 
diff --git a/src/test/unit/System.Windows.Forms/System/Windows/Forms/ListBox.IntegerCollectionTests.cs b/src/test/unit/System.Windows.Forms/System/Windows/Forms/ListBox.IntegerCollectionTests.cs
index 6912f58e31f..b9e110f0fca 100644
--- a/src/test/unit/System.Windows.Forms/System/Windows/Forms/ListBox.IntegerCollectionTests.cs
+++ b/src/test/unit/System.Windows.Forms/System/Windows/Forms/ListBox.IntegerCollectionTests.cs
@@ -30,7 +30,7 @@ public void ListBoxIntegerCollection_ICollection_Properties_GetReturnsExpected()
         using ListBox owner = new();
         ICollection collection = new ListBox.IntegerCollection(owner);
         Assert.Empty(collection);
-        Assert.True(collection.IsSynchronized);
+        Assert.False(collection.IsSynchronized);
         Assert.Same(collection, collection.SyncRoot);
     }
 
@@ -42,7 +42,7 @@ public void ListBoxIntegerCollection_IList_Properties_GetReturnsExpected()
         Assert.Empty(collection);
         Assert.False(collection.IsFixedSize);
         Assert.False(collection.IsReadOnly);
-        Assert.True(collection.IsSynchronized);
+        Assert.False(collection.IsSynchronized);
         Assert.Same(collection, collection.SyncRoot);
     }
 
diff --git a/src/test/unit/System.Windows.Forms/System/Windows/Forms/ListBox.SelectedIndexCollectionTests.cs b/src/test/unit/System.Windows.Forms/System/Windows/Forms/ListBox.SelectedIndexCollectionTests.cs
index e589d76f7f3..1cb76f08f53 100644
--- a/src/test/unit/System.Windows.Forms/System/Windows/Forms/ListBox.SelectedIndexCollectionTests.cs
+++ b/src/test/unit/System.Windows.Forms/System/Windows/Forms/ListBox.SelectedIndexCollectionTests.cs
@@ -29,7 +29,7 @@ public void ListBoxSelectedIndexCollection_ICollection_Properties_GetReturnsExpe
         using ListBox owner = new();
         ICollection collection = new ListBox.SelectedIndexCollection(owner);
         Assert.Empty(collection);
-        Assert.True(collection.IsSynchronized);
+        Assert.False(collection.IsSynchronized);
         Assert.Same(collection, collection.SyncRoot);
     }
 
@@ -41,7 +41,7 @@ public void ListBoxSelectedIndexCollection_IList_Properties_GetReturnsExpected()
         Assert.Empty(collection);
         Assert.True(collection.IsFixedSize);
         Assert.True(collection.IsReadOnly);
-        Assert.True(collection.IsSynchronized);
+        Assert.False(collection.IsSynchronized);
         Assert.Same(collection, collection.SyncRoot);
     }