diff --git a/lib/searchkick.rb b/lib/searchkick.rb
index e96f9c2..76cc381 100644
--- a/lib/searchkick.rb
+++ b/lib/searchkick.rb
@@ -12,6 +12,7 @@ require "forwardable"
 # modules
 require "searchkick/controller_runtime"
 require "searchkick/index"
+require "searchkick/index_cache"
 require "searchkick/index_options"
 require "searchkick/indexer"
 require "searchkick/hash_wrapper"
diff --git a/lib/searchkick/index_cache.rb b/lib/searchkick/index_cache.rb
new file mode 100644
index 0000000..cd6ac53
--- /dev/null
+++ b/lib/searchkick/index_cache.rb
@@ -0,0 +1,30 @@
+module Searchkick
+  class IndexCache
+    def initialize(max_size: 20)
+      @data = {}
+      @mutex = Mutex.new
+      @max_size = max_size
+    end
+
+    # probably a better pattern for this
+    # but keep it simple
+    def fetch(name)
+      # thread-safe in MRI without mutex
+      # due to how context switching works
+      @mutex.synchronize do
+        if @data.key?(name)
+          @data[name]
+        else
+          @data.clear if @data.size >= @max_size
+          @data[name] = yield
+        end
+      end
+    end
+
+    def clear
+      @mutex.synchronize do
+        @data.clear
+      end
+    end
+  end
+end
diff --git a/lib/searchkick/model.rb b/lib/searchkick/model.rb
index 4776fd7..cecdf56 100644
--- a/lib/searchkick/model.rb
+++ b/lib/searchkick/model.rb
@@ -55,7 +55,7 @@ module Searchkick
 
         class_variable_set :@@searchkick_options, options.dup
         class_variable_set :@@searchkick_klass, self
-        class_variable_set :@@searchkick_index_cache, {}
+        class_variable_set :@@searchkick_index_cache, Searchkick::IndexCache.new
 
         class << self
           def searchkick_search(term = "*", **options, &block)
@@ -71,7 +71,7 @@ module Searchkick
             index = name || searchkick_index_name
             index = index.call if index.respond_to?(:call)
             index_cache = class_variable_get(:@@searchkick_index_cache)
-            index_cache[index] ||= Searchkick::Index.new(index, searchkick_options)
+            index_cache.fetch(index) { Searchkick::Index.new(index, searchkick_options) }
           end
           alias_method :search_index, :searchkick_index unless method_defined?(:search_index)
 
diff --git a/test/index_cache_test.rb b/test/index_cache_test.rb
new file mode 100644
index 0000000..42aed2e
--- /dev/null
+++ b/test/index_cache_test.rb
@@ -0,0 +1,49 @@
+require_relative "test_helper"
+
+class IndexCacheTest < Minitest::Test
+  def setup
+    Product.class_variable_get(:@@searchkick_index_cache).clear
+  end
+
+  def test_default
+    object_id = Product.search_index.object_id
+    3.times do
+      assert_equal object_id, Product.search_index.object_id
+    end
+  end
+
+  def test_max_size
+    starting_ids = object_ids(20)
+    assert_equal starting_ids, object_ids(20)
+    Product.search_index(name: "other")
+    refute_equal starting_ids, object_ids(20)
+  end
+
+  def test_thread_safe
+    object_ids = with_threads { object_ids(20) }
+    assert_equal object_ids[0], object_ids[1]
+    assert_equal object_ids[0], object_ids[2]
+  end
+
+  # object ids can differ since threads progress at different speeds
+  # test to make sure doesn't crash
+  def test_thread_safe_max_size
+    with_threads { object_ids(1000) }
+  end
+
+  private
+
+  def object_ids(count)
+    count.times.map { |i| Product.search_index(name: "index#{i}").object_id }
+  end
+
+  def with_threads
+    previous = Thread.report_on_exception
+    begin
+      Thread.report_on_exception = true
+      3.times.map { Thread.new { yield } }.map(&:join).map(&:value)
+    ensure
+      Thread.report_on_exception = previous
+    end
+  end
+end
--
libgit2 0.21.0