diff --git a/lib/active_record_doctor/detectors/missing_non_null_constraint.rb b/lib/active_record_doctor/detectors/missing_non_null_constraint.rb
index 5f4283f..a7293e9 100644
--- a/lib/active_record_doctor/detectors/missing_non_null_constraint.rb
+++ b/lib/active_record_doctor/detectors/missing_non_null_constraint.rb
@@ -32,6 +32,9 @@ def detect
             model.abstract_class? || sti_base_model?(model)
           end
 
+          # There are no STI child models.
+          concrete_models = models if concrete_models.empty?
+
           connection.columns(table).each do |column|
             next if config(:ignore_columns).include?("#{table}.#{column.name}")
             next if !column.null
diff --git a/test/active_record_doctor/detectors/missing_non_null_constraint_test.rb b/test/active_record_doctor/detectors/missing_non_null_constraint_test.rb
index 38ecf35..b0f728f 100644
--- a/test/active_record_doctor/detectors/missing_non_null_constraint_test.rb
+++ b/test/active_record_doctor/detectors/missing_non_null_constraint_test.rb
@@ -187,6 +187,14 @@ def test_optional_columns_validated_by_some_non_sti_models_are_allowed
     refute_problems
   end
 
+  def test_optional_columns_validated_by_sti_parent_without_child_is_allowed
+    create_table(:users) do |t|
+      t.string :type
+    end.define_model
+
+    refute_problems
+  end
+
   def test_not_null_check_constraint
     skip unless postgresql?