diff --git a/lib/rdoc/store.rb b/lib/rdoc/store.rb
index 50bd25021d..563a9c96df 100644
--- a/lib/rdoc/store.rb
+++ b/lib/rdoc/store.rb
@@ -182,6 +182,7 @@ def add_file(absolute_name, relative_name: absolute_name, parser: nil)
         top_level.store = self
         @files_hash[relative_name] = top_level
         @text_files_hash[relative_name] = top_level if top_level.text?
+        @page_index = nil
       end
 
       top_level
@@ -204,6 +205,7 @@ def remove_file(relative_name)
       @c_singleton_class_variables.delete(relative_name)
       return unless top_level
 
+      @page_index = nil
       remove_classes_and_modules(top_level.classes_or_modules)
     end
 
@@ -743,6 +745,7 @@ def load_all
         end
       end
 
+      @page_index = nil
       @cache[:pages].each do |page_name|
         page = load_page page_name
         @files_hash[page_name] = page
@@ -912,9 +915,12 @@ def modules_hash
     # Returns the RDoc::TopLevel that is a file and has the given +name+
 
     def page(name)
-      @files_hash.each_value.find do |file|
-        file.page_name == name or file.base_name == name
+      @page_index ||= @files_hash.each_value.each_with_object({}) do |file, index|
+        index[file.page_name] ||= file
+        index[file.base_name] ||= file
       end
+
+      @page_index[name]
     end
 
     ##
diff --git a/test/rdoc/rdoc_store_test.rb b/test/rdoc/rdoc_store_test.rb
index 00fc44ac9f..6caccdc7b5 100644
--- a/test/rdoc/rdoc_store_test.rb
+++ b/test/rdoc/rdoc_store_test.rb
@@ -650,6 +650,45 @@ def test_page_with_extension
     assert_equal page, @store.page('PAGE.txt')
   end
 
+  def test_page_index_linear_performance
+    assert_linear_performance((1..4).map { |i| 10**i }) do |count|
+      store = RDoc::Store.new RDoc::Options.new
+      count.times { |i| store.add_file "page_#{i}.txt" }
+
+      count.times do
+        store.page 'page_0'
+        store.page 'missing'
+      end
+    end
+  end
+
+  def test_page_index_invalidated_when_files_change
+    assert_nil @store.page('PAGE')
+
+    first_page = @store.add_file 'PAGE.txt', parser: RDoc::Parser::Simple
+    assert_same first_page, @store.page('PAGE')
+
+    second_page = @store.add_file 'doc/PAGE.md', parser: RDoc::Parser::Simple
+    assert_same first_page, @store.page('PAGE')
+
+    @store.remove_file 'PAGE.txt'
+    assert_same second_page, @store.page('PAGE')
+  end
+
+  def test_page_index_invalidated_by_load_all
+    FileUtils.mkdir_p @tmpdir
+    source = RDoc::Store.new RDoc::Options.new, path: @tmpdir
+    source.add_file 'README.txt', parser: RDoc::Parser::Simple
+    source.save
+
+    loaded = RDoc::Store.new RDoc::Options.new, path: @tmpdir
+    assert_nil loaded.page('README')
+
+    loaded.load_all
+
+    assert_equal 'README.txt', loaded.page('README').relative_name
+  end
+
   def test_save
     FileUtils.mkdir_p @tmpdir