diff --git a/lib/bundler/stub_specification.rb b/lib/bundler/stub_specification.rb
index d5f6a883f97..aeacf245a35 100644
--- a/lib/bundler/stub_specification.rb
+++ b/lib/bundler/stub_specification.rb
@@ -4,6 +4,7 @@
 module Bundler
   class StubSpecification < RemoteSpecification
     def self.from_stub(stub)
+      return stub if stub.is_a?(Bundler::StubSpecification)
       spec = new(stub.name, stub.version, stub.platform, nil)
       spec.stub = stub
       spec
diff --git a/spec/bundler/stub_specification_spec.rb b/spec/bundler/stub_specification_spec.rb
new file mode 100644
index 00000000000..f1ddf43bb43
--- /dev/null
+++ b/spec/bundler/stub_specification_spec.rb
@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+require "spec_helper"
+
+RSpec.describe Bundler::StubSpecification do
+  let(:gemspec) do
+    Gem::Specification.new do |s|
+      s.name = "gemname"
+      s.version = "1.0.0"
+      s.loaded_from = __FILE__
+    end
+  end
+
+  let(:with_bundler_stub_spec) do
+    described_class.from_stub(gemspec)
+  end
+
+  if Bundler.rubygems.provides?(">= 2.1")
+    describe "#from_stub" do
+      it "returns the same stub if already a Bundler::StubSpecification" do
+        stub = described_class.from_stub(with_bundler_stub_spec)
+        expect(stub).to be(with_bundler_stub_spec)
+      end
+    end
+  end
+end