diff --git a/features/core_standalone.feature b/features/core_standalone.feature
index a583563dae..53523d9abf 100644
--- a/features/core_standalone.feature
+++ b/features/core_standalone.feature
@@ -5,6 +5,8 @@ Feature: Use rspec-core without rspec-mocks or rspec-expectations
   available, but rspec-core can be used just fine without either of those
   gems installed.
 
+  # Rubinius stacktrace includes kernel/loader.rb etc.
+  @unsupported-on-rbx
   Scenario: Use only rspec-core when only it is installed
     Given only rspec-core is installed
       And a file named "core_only_spec.rb" with:
diff --git a/spec/rspec/core/formatters/documentation_formatter_spec.rb b/spec/rspec/core/formatters/documentation_formatter_spec.rb
index 43eac1beaa..2c14d8d2cc 100644
--- a/spec/rspec/core/formatters/documentation_formatter_spec.rb
+++ b/spec/rspec/core/formatters/documentation_formatter_spec.rb
@@ -77,8 +77,8 @@ def execution_result(values)
 ")
     end
 
-    # The backrace is slightly different on JRuby so we skip there.
-    it 'produces the expected full output', :unless => RUBY_PLATFORM == 'java' do
+    # The backtrace is slightly different on JRuby/Rubinius so we skip there.
+    it 'produces the expected full output', :if => RSpec::Support::Ruby.mri? do
       output = run_example_specs_with_formatter("doc")
       output.gsub!(/ +$/, '') # strip trailing whitespace
 
diff --git a/spec/rspec/core/formatters/progress_formatter_spec.rb b/spec/rspec/core/formatters/progress_formatter_spec.rb
index a92a9fdb0f..9386b6b1c4 100644
--- a/spec/rspec/core/formatters/progress_formatter_spec.rb
+++ b/spec/rspec/core/formatters/progress_formatter_spec.rb
@@ -40,8 +40,8 @@
     expect(output.string).to eq("\n")
   end
 
-  # The backrace is slightly different on JRuby so we skip there.
-  it 'produces the expected full output', :unless => RUBY_PLATFORM == 'java' do
+  # The backtrace is slightly different on JRuby/Rubinius so we skip there.
+  it 'produces the expected full output', :if => RSpec::Support::Ruby.mri? do
     output = run_example_specs_with_formatter("progress")
     output.gsub!(/ +$/, '') # strip trailing whitespace