diff --git a/spec/mspec/lib/mspec/guards/platform.rb b/spec/mspec/lib/mspec/guards/platform.rb
index c69401ea39..2d22d4fb59 100644
--- a/spec/mspec/lib/mspec/guards/platform.rb
+++ b/spec/mspec/lib/mspec/guards/platform.rb
@@ -6,10 +6,8 @@ class PlatformGuard < SpecGuard
       case name
       when :rubinius
         RUBY_ENGINE.start_with?('rbx')
-      when :ruby, :jruby, :truffleruby, :ironruby, :macruby, :maglev, :topaz, :opal
-        RUBY_ENGINE.start_with?(name.to_s)
       else
-        raise "unknown implementation #{name}"
+        RUBY_ENGINE.start_with?(name.to_s)
       end
     end
   end
diff --git a/spec/mspec/spec/guards/platform_spec.rb b/spec/mspec/spec/guards/platform_spec.rb
index ad1e3695ca..6088fb2ba6 100644
--- a/spec/mspec/spec/guards/platform_spec.rb
+++ b/spec/mspec/spec/guards/platform_spec.rb
@@ -165,11 +165,10 @@ describe PlatformGuard, ".implementation?" do
     PlatformGuard.implementation?(:ruby).should == true
   end
 
-  it "raises an error when passed an unrecognized name" do
-    stub_const 'RUBY_ENGINE', 'ruby'
-    lambda {
-      PlatformGuard.implementation?(:python)
-    }.should raise_error(/unknown implementation/)
+  it "works for an unrecognized name" do
+    stub_const 'RUBY_ENGINE', 'myrubyimplementation'
+    PlatformGuard.implementation?(:myrubyimplementation).should == true
+    PlatformGuard.implementation?(:other).should == false
   end
 end