diff --git a/lib/mongoid/config.rb b/lib/mongoid/config.rb
index fb04d016d0..aac4ff63fe 100644
--- a/lib/mongoid/config.rb
+++ b/lib/mongoid/config.rb
@@ -180,19 +180,6 @@ module Config
     # See https://jira.mongodb.org/browse/MONGOID-5785 for more details.
     option :allow_scopes_to_unset_default_scope, default: false
 
-    # When this flag is false, indexes are (roughly) validated on the client
-    # to prevent duplicate indexes being declared. This validation is
-    # incomplete, however, and can result in some indexes being silently
-    # ignored.
-    #
-    # Setting this to true will allow duplicate indexes to be declared and sent
-    # to the server. The server will then validate the indexes and raise an
-    # exception if duplicates are detected.
-    #
-    # See https://jira.mongodb.org/browse/MONGOID-5827 for an example of the
-    # consequences of duplicate index checking.
-    option :allow_duplicate_index_declarations, default: false
-
     # Returns the Config singleton, for use in the configure DSL.
     #
     # @return [ self ] The Config singleton.
diff --git a/lib/mongoid/indexable.rb b/lib/mongoid/indexable.rb
index fc19bed16a..8eb6b7e1b3 100644
--- a/lib/mongoid/indexable.rb
+++ b/lib/mongoid/indexable.rb
@@ -95,13 +95,7 @@ def add_indexes
       # @return [ Hash ] The index options.
       def index(spec, options = nil)
         specification = Specification.new(self, spec, options)
-
-        # the equality test for Indexable::Specification instances does not
-        # consider any options, which means names are not compared. This means
-        # that an index with different options from another, and a different
-        # name, will be silently ignored unless duplicate index declarations
-        # are allowed.
-        if Mongoid.allow_duplicate_index_declarations || !index_specifications.include?(specification)
+        if !index_specifications.include?(specification)
           index_specifications.push(specification)
         end
       end
@@ -116,8 +110,9 @@ def index(spec, options = nil)
       #
       # @return [ Specification ] The found specification.
       def index_specification(index_hash, index_name = nil)
+        index = OpenStruct.new(fields: index_hash.keys, key: index_hash)
         index_specifications.detect do |spec|
-          spec.superficial_match?(key: index_hash, name: index_name)
+          spec == index || (index_name && index_name == spec.name)
         end
       end
 
diff --git a/lib/mongoid/indexable/specification.rb b/lib/mongoid/indexable/specification.rb
index da7504e6e6..ee707c52cf 100644
--- a/lib/mongoid/indexable/specification.rb
+++ b/lib/mongoid/indexable/specification.rb
@@ -30,25 +30,7 @@ class Specification
       #
       # @return [ true | false ] If the specs are equal.
       def ==(other)
-        superficial_match?(key: other.key)
-      end
-
-      # Performs a superficial comparison with the given criteria, checking
-      # only the key and (optionally) the name. Options are not compared.
-      #
-      # Note that the ordering of the fields in the key is significant. Two
-      # keys with different orderings will not match, here.
-      #
-      # @param [ Hash ] key the key that defines the index.
-      # @param [ String | nil ] name the name given to the index, or nil to
-      #    ignore the name.
-      #
-      # @return [ true | false ] the result of the comparison, true if this
-      #   specification matches the criteria, and false otherwise.
-      def superficial_match?(key: {}, name: nil)
-        (name && name == self.name) ||
-          self.fields == key.keys &&
-          self.key == key
+        fields == other.fields && key == other.key
       end
 
       # Instantiate a new index specification.
diff --git a/spec/mongoid/indexable_spec.rb b/spec/mongoid/indexable_spec.rb
index f46916536c..4eb9e7f6ba 100644
--- a/spec/mongoid/indexable_spec.rb
+++ b/spec/mongoid/indexable_spec.rb
@@ -959,61 +959,5 @@ def self.hereditary?
         end
       end
     end
-
-    context 'when declaring a duplicate index with different options' do
-      def declare_duplicate_indexes!
-        klass.index({ name: 1 }, { partial_filter_expression: { name: 'a' } })
-        klass.index({ name: 1 }, { partial_filter_expression: { name: 'b' } })
-        klass.create_indexes
-      end
-
-      context 'when allow_duplicate_index_declarations is false' do
-        config_override :allow_duplicate_index_declarations, false
-
-        it 'silently ignores the duplicate definition' do
-          expect { declare_duplicate_indexes! }.not_to raise_exception
-        end
-      end
-
-      context 'when allow_duplicate_index_declarations is true' do
-        config_override :allow_duplicate_index_declarations, true
-
-        it 'raises a server error' do
-          expect { declare_duplicate_indexes! }.to raise_exception
-        end
-      end
-    end
-
-    context 'when declaring a duplicate index with different names' do
-      def declare_duplicate_indexes!
-        klass.index({ name: 1 }, { partial_filter_expression: { name: 'a' } })
-        klass.index({ name: 1 }, { name: 'alt_name', partial_filter_expression: { name: 'b' } })
-        klass.create_indexes
-      end
-
-      let(:index_count) { klass.collection.indexes.count }
-
-
-      context 'when allow_duplicate_index_declarations is false' do
-        config_override :allow_duplicate_index_declarations, false
-
-        it 'silently ignores the duplicate definition' do
-          expect { declare_duplicate_indexes! }.not_to raise_exception
-          expect(index_count).to be == 2 # _id and name
-        end
-      end
-
-      context 'when allow_duplicate_index_declarations is true' do
-        # 4.4 apparently doesn't recognize :name option for indexes?
-        min_server_version '5.0'
-
-        config_override :allow_duplicate_index_declarations, true
-
-        it 'creates both indexes' do
-          expect { declare_duplicate_indexes! }.not_to raise_exception
-          expect(index_count).to be == 3 # _id, name, alt_name
-        end
-      end
-    end
   end
 end