diff --git a/CHANGELOG.md b/CHANGELOG.md
index bc675d2e..9bd5be39 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,7 @@
 
 * Ruby 4.0 support (no changes required)
 * Support procs on validators for minlength/maxlength, and improve validators logic across the board to match Rails [#1859](https://github.com/heartcombo/simple_form/pull/1859)
+* Fix label `for` attribute not matching input `id` when collection contains a nil value [#1840](https://github.com/heartcombo/simple_form/issues/1840)
 
 ## 5.4.0
 
diff --git a/lib/simple_form/tags.rb b/lib/simple_form/tags.rb
index 2d779b0d..fed27ba0 100644
--- a/lib/simple_form/tags.rb
+++ b/lib/simple_form/tags.rb
@@ -26,6 +26,20 @@ def render_collection
         end.join.html_safe
       end
 
+      # Override Rails' sanitize_attribute_name to avoid generating a trailing
+      # underscore when the collection value is nil (e.g. "method_" instead of
+      # "method"), which causes the label's `for` attribute to not match the
+      # input's `id`. See https://github.com/heartcombo/simple_form/issues/1840
+      def sanitize_attribute_name(value)
+        sanitized = sanitized_value(value)
+
+        if sanitized.empty?
+          sanitized_method_name.dup
+        else
+          "#{sanitized_method_name}_#{sanitized}"
+        end
+      end
+
       def wrap_rendered_collection(collection)
         wrapper_tag = @options[:collection_wrapper_tag]
 
diff --git a/test/inputs/collection_check_boxes_input_test.rb b/test/inputs/collection_check_boxes_input_test.rb
index 139ac33f..03d0e274 100644
--- a/test/inputs/collection_check_boxes_input_test.rb
+++ b/test/inputs/collection_check_boxes_input_test.rb
@@ -314,4 +314,24 @@ class CollectionCheckBoxesInputTest < ActionView::TestCase
       assert_select 'label.beautiful-label', count: 2
     end
   end
+
+  test 'input check boxes label for attribute matches input id when collection contains nil value' do
+    with_input_for @user, :name, :check_boxes, collection: [['Yes', true], ['Undefined', nil]]
+
+    assert_select 'input[type=checkbox][value=true]#user_name_true'
+    assert_select 'label.collection_check_boxes[for=user_name_true]', 'Yes'
+    assert_select 'input[type=checkbox]#user_name'
+    assert_select 'label.collection_check_boxes[for=user_name]', 'Undefined'
+    assert_no_select 'label[for=user_name_]'
+  end
+
+  test 'input check boxes with nested style label for attribute matches input id when collection contains nil value' do
+    swap SimpleForm, boolean_style: :nested do
+      with_input_for @user, :name, :check_boxes, collection: [['Yes', true], ['Undefined', nil]]
+
+      assert_select 'label[for=user_name_true]'
+      assert_select 'label[for=user_name]'
+      assert_no_select 'label[for=user_name_]'
+    end
+  end
 end
diff --git a/test/inputs/collection_radio_buttons_input_test.rb b/test/inputs/collection_radio_buttons_input_test.rb
index 94c5aaaa..2b75fcb6 100644
--- a/test/inputs/collection_radio_buttons_input_test.rb
+++ b/test/inputs/collection_radio_buttons_input_test.rb
@@ -437,4 +437,24 @@ class CollectionRadioButtonsInputTest < ActionView::TestCase
       assert_select 'label.beautiful-label', count: 2
     end
   end
+
+  test 'input radio label for attribute matches input id when collection contains nil value' do
+    with_input_for @user, :name, :radio_buttons, collection: [['Yes', true], ['Undefined', nil]]
+
+    assert_select 'input[type=radio][value=true]#user_name_true'
+    assert_select 'label.collection_radio_buttons[for=user_name_true]', 'Yes'
+    assert_select 'input[type=radio]#user_name'
+    assert_select 'label.collection_radio_buttons[for=user_name]', 'Undefined'
+    assert_no_select 'label[for=user_name_]'
+  end
+
+  test 'input radio with nested style label for attribute matches input id when collection contains nil value' do
+    swap SimpleForm, boolean_style: :nested do
+      with_input_for @user, :name, :radio_buttons, collection: [['Yes', true], ['Undefined', nil]]
+
+      assert_select 'label[for=user_name_true]'
+      assert_select 'label[for=user_name]'
+      assert_no_select 'label[for=user_name_]'
+    end
+  end
 end