diff --git a/lib/mongoid/association/referenced/has_many/proxy.rb b/lib/mongoid/association/referenced/has_many/proxy.rb
index 23576873a8..fc1f3efc58 100644
--- a/lib/mongoid/association/referenced/has_many/proxy.rb
+++ b/lib/mongoid/association/referenced/has_many/proxy.rb
@@ -259,10 +259,14 @@ def exists?(id_or_conditions = :none)
           # @yield [ Object ] Yields each enumerable element to the block.
           #
           # @return [ Document | Array<Document> | nil ] A document or matching documents.
-          def find(...)
-            matching = criteria.find(...)
-            Array(matching).each { |doc| _target.push(doc) }
-            matching
+          def find(*args, &block)
+            if block_given? && args.empty?
+              detect(&block)
+            else
+              matching = criteria.find(*args, &block)
+              Array(matching).each { |doc| _target.push(doc) }
+              matching
+            end
           end
 
           # Removes all associations between the base document and the target
diff --git a/spec/mongoid/association/referenced/has_many/proxy_spec.rb b/spec/mongoid/association/referenced/has_many/proxy_spec.rb
index 1b8e2fa36d..fdd853d590 100644
--- a/spec/mongoid/association/referenced/has_many/proxy_spec.rb
+++ b/spec/mongoid/association/referenced/has_many/proxy_spec.rb
@@ -2246,6 +2246,23 @@ def with_transaction_via(model, &block)
           end
         ).to be_nil
       end
+
+      context 'when the parent is not persisted (MONGOID-5759)' do
+        let(:person) { Person.new }
+        let!(:post) { person.posts.build(title: 'unpersisted post') }
+
+        it 'yields unpersisted built documents' do
+          expect(
+            person.posts.find { |p| p.title == 'unpersisted post' }
+          ).to eq(post)
+        end
+
+        it 'returns nil when no match among unpersisted documents' do
+          expect(
+            person.posts.find { |p| p.title == 'other' }
+          ).to be_nil
+        end
+      end
     end
   end