diff --git a/lib/bundler/remote_specification.rb b/lib/bundler/remote_specification.rb
index 89b69e1045..4e966b820a 100644
--- a/lib/bundler/remote_specification.rb
+++ b/lib/bundler/remote_specification.rb
@@ -27,6 +27,13 @@ module Bundler
       @platform = _remote_specification.platform
     end
 
+    # A fallback is included because the original version of the specification
+    # API didn't include that field, so some marshalled specs in the index have it
+    # set to +nil+.
+    def required_rubygems_version
+      @required_rubygems_version ||= _remote_specification.required_rubygems_version || Gem::Requirement.default
+    end
+
     def full_name
       if platform == Gem::Platform::RUBY || platform.nil?
         "#{@name}-#{@version}"
diff --git a/spec/bundler/install/gemfile/sources_spec.rb b/spec/bundler/install/gemfile/sources_spec.rb
index 5456e95f33..26ecb840c7 100644
--- a/spec/bundler/install/gemfile/sources_spec.rb
+++ b/spec/bundler/install/gemfile/sources_spec.rb
@@ -1443,4 +1443,57 @@ RSpec.describe "bundle install with gems on multiple sources" do
       L
     end
   end
+
+  context "when default source includes old gems with nil required_rubygems_version" do
+    before do
+      build_repo2 do
+        build_gem "ruport", "1.7.0.3" do |s|
+          s.add_dependency "pdf-writer", "1.1.8"
+        end
+      end
+
+      build_repo gem_repo4 do
+        build_gem "pdf-writer", "1.1.8"
+      end
+
+      path = "#{gem_repo4}/#{Gem::MARSHAL_SPEC_DIR}/pdf-writer-1.1.8.gemspec.rz"
+      spec = Marshal.load(Bundler.rubygems.inflate(File.binread(path)))
+      spec.instance_variable_set(:@required_rubygems_version, nil)
+      File.open(path, "wb") do |f|
+        f.write Gem.deflate(Marshal.dump(spec))
+      end
+
+      gemfile <<~G
+        source "https://localgemserver.test"
+
+        gem "ruport", "= 1.7.0.3", :source => "https://localgemserver.test/extra"
+      G
+    end
+
+    it "handles that fine" do
+      bundle "install", :artifice => "compact_index_extra", :env => { "BUNDLER_SPEC_GEM_REPO" => gem_repo4.to_s }
+
+      expect(lockfile).to eq <<~L
+        GEM
+          remote: https://localgemserver.test/
+          specs:
+            pdf-writer (1.1.8)
+
+        GEM
+          remote: https://localgemserver.test/extra/
+          specs:
+            ruport (1.7.0.3)
+              pdf-writer (= 1.1.8)
+
+        PLATFORMS
+          #{specific_local_platform}
+
+        DEPENDENCIES
+          ruport (= 1.7.0.3)!
+
+        BUNDLED WITH
+           #{Bundler::VERSION}
+      L
+    end
+  end
 end