diff --git a/lib/rspec/support/warnings.rb b/lib/rspec/support/warnings.rb
index 2acd27920..d21da16ba 100644
--- a/lib/rspec/support/warnings.rb
+++ b/lib/rspec/support/warnings.rb
@@ -1,6 +1,6 @@
 module RSpec
 
-  if self.const_get("Core")
+  if defined?(::RSpec::Core)
 
     # @private
     #
diff --git a/spec/rspec/warnings_spec.rb b/spec/rspec/warnings_spec.rb
index a31b932c3..b3fa2739d 100644
--- a/spec/rspec/warnings_spec.rb
+++ b/spec/rspec/warnings_spec.rb
@@ -1,4 +1,5 @@
 require "spec_helper"
+require 'rspec/support/spec/in_sub_process'
 
 # Make sure we're using the `rspec-support` CallerFilter
 # can be removed at a later date
@@ -27,61 +28,66 @@ class << self
 end
 # end warnings cleanup #
 
-require 'rspec/support/warnings'
-
 describe "rspec warnings and deprecations" do
+  include RSpec::Support::InSubProcess
 
-  def reset_and_load_warnings
-    RSpec.module_eval do
-      class << self
-        undef deprecate        if defined?(RSpec.deprecate)
-        undef warn_deprecation if defined?(RSpec.warn_deprecation)
-        undef warning          if defined?(RSpec.warning)
-        undef warn_with        if defined?(RSpec.warn_with)
-      end
+  def run_with_rspec_core
+    in_sub_process do
+      load 'rspec/support/warnings.rb'
+      yield
     end
-    load 'rspec/support/warnings.rb'
   end
 
-  context "when rspec-core is available" do
-    before do
-      reset_and_load_warnings
+  def run_without_rspec_core
+    in_sub_process do
+      hide_const "::RSpec::Core"
+      load 'rspec/support/warnings.rb'
+      yield
     end
+  end
+
+  context "when rspec-core is available" do
     describe "#deprecate" do
       it "passes the hash to the reporter" do
-        expect(RSpec.configuration.reporter).to receive(:deprecation).with(hash_including :deprecated => "deprecated_method", :replacement => "replacement")
-        RSpec.deprecate("deprecated_method", :replacement => "replacement")
+        run_with_rspec_core do
+          expect(RSpec.configuration.reporter).to receive(:deprecation).with(hash_including :deprecated => "deprecated_method", :replacement => "replacement")
+          RSpec.deprecate("deprecated_method", :replacement => "replacement")
+        end
       end
 
       it "adds the call site" do
-        expect_deprecation_with_call_site(__FILE__, __LINE__ + 1)
-        RSpec.deprecate("deprecated_method")
+        run_with_rspec_core do
+          expect_deprecation_with_call_site(__FILE__, __LINE__ + 1)
+          RSpec.deprecate("deprecated_method")
+        end
       end
 
       it "doesn't override a passed call site" do
-        expect_deprecation_with_call_site("some_file.rb", 17)
-        RSpec.deprecate("deprecated_method", :call_site => "/some_file.rb:17")
+        run_with_rspec_core do
+          expect_deprecation_with_call_site("some_file.rb", 17)
+          RSpec.deprecate("deprecated_method", :call_site => "/some_file.rb:17")
+        end
       end
     end
 
     describe "#warn_deprecation" do
       it "puts message in a hash" do
-        expect(RSpec.configuration.reporter).to receive(:deprecation).with(hash_including :message => "this is the message")
-        RSpec.warn_deprecation("this is the message")
+        run_with_rspec_core do
+          expect(RSpec.configuration.reporter).to receive(:deprecation).with(hash_including :message => "this is the message")
+          RSpec.warn_deprecation("this is the message")
+        end
       end
     end
   end
 
   context "when rspec-core is not available" do
-    before do
-      allow(RSpec).to receive(:const_get).with("Core")
-      reset_and_load_warnings
-    end
 
     shared_examples_for "falls back to warn for" do |method|
       it 'falls back to warning with a plain message' do
-        expect(::Kernel).to receive(:warn).with /message/
-        RSpec.send(method,'message')
+        run_without_rspec_core do
+          expect(::Kernel).to receive(:warn).with /message/
+          RSpec.send(method,'message')
+        end
       end
     end
 
@@ -91,20 +97,26 @@ class << self
 
   shared_examples_for "warning helper" do |helper|
     it 'warns with the message text' do
-      expect(::Kernel).to receive(:warn).with(/Message/)
-      RSpec.send(helper, 'Message')
+      run_without_rspec_core do
+        expect(::Kernel).to receive(:warn).with(/Message/)
+        RSpec.send(helper, 'Message')
+      end
     end
 
     it 'sets the calling line' do
-      expect(::Kernel).to receive(:warn).with(/#{__FILE__}:#{__LINE__+1}/)
-      RSpec.send(helper, 'Message')
+      run_without_rspec_core do
+        expect(::Kernel).to receive(:warn).with(/#{__FILE__}:#{__LINE__+1}/)
+        RSpec.send(helper, 'Message')
+      end
     end
   end
 
   describe "#warning" do
     it 'prepends WARNING:' do
-      expect(::Kernel).to receive(:warn).with(/WARNING: Message\./)
-      RSpec.warning 'Message'
+      run_without_rspec_core do
+        expect(::Kernel).to receive(:warn).with(/WARNING: Message\./)
+        RSpec.warning 'Message'
+      end
     end
     it_should_behave_like 'warning helper', :warning
   end