diff --git a/NEWS.md b/NEWS.md
index cf554860..bbf2f31e 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -5,6 +5,10 @@
 
 * Add ability to test `:autosave` option on associations.
 
+* Fix `validate_uniqueness_of(...).allow_nil` so that it can be used against an
+  non-password attribute which is in a model that `has_secure_password`. Doing
+  so previously would result in a "Password digest missing on new record" error.
+
 # v 2.5.0
 
 * Fix Rails/Test::Unit integration to ensure that the test case classes we are
diff --git a/lib/shoulda/matchers/active_model/validate_uniqueness_of_matcher.rb b/lib/shoulda/matchers/active_model/validate_uniqueness_of_matcher.rb
index 50b4ed38..4f074ce3 100644
--- a/lib/shoulda/matchers/active_model/validate_uniqueness_of_matcher.rb
+++ b/lib/shoulda/matchers/active_model/validate_uniqueness_of_matcher.rb
@@ -115,10 +115,18 @@ module Shoulda # :nodoc:
 
           @subject.class.new.tap do |instance|
             instance.send("#{@attribute}=", value)
+            if has_secure_password?
+              instance.password = 'password'
+              instance.password_confirmation = 'password'
+            end
             instance.save(validate: false)
           end
         end
 
+        def has_secure_password?
+          @subject.class.ancestors.map(&:to_s).include?('ActiveModel::SecurePassword::InstanceMethodsOnActivation')
+        end
+
         def set_scoped_attributes
           if @options[:scopes].present?
             @options[:scopes].all? do |scope|
diff --git a/spec/shoulda/matchers/active_model/validate_uniqueness_of_matcher_spec.rb b/spec/shoulda/matchers/active_model/validate_uniqueness_of_matcher_spec.rb
index 70689ef8..7c28f880 100644
--- a/spec/shoulda/matchers/active_model/validate_uniqueness_of_matcher_spec.rb
+++ b/spec/shoulda/matchers/active_model/validate_uniqueness_of_matcher_spec.rb
@@ -293,6 +293,18 @@ describe Shoulda::Matchers::ActiveModel::ValidateUniquenessOfMatcher do
       end
     end
 
+    if active_model_3_1?
+      context 'when the subject has a secure password' do
+        it 'allows nil on the attribute' do
+          model = define_model(:example, attr: :string, password_digest: :string) do |m|
+            validates_uniqueness_of :attr, allow_nil: true
+            has_secure_password
+          end.new
+          expect(model).to matcher.allow_nil
+        end
+      end
+    end
+
     it "should create a nil and verify that it is allowed" do
       model = define_model_with_allow_nil
       expect(model).to matcher.allow_nil