diff --git a/packages/exo/test/test-heap-classes.js b/packages/exo/test/test-heap-classes.js
index c81f650357..61716b4a52 100644
--- a/packages/exo/test/test-heap-classes.js
+++ b/packages/exo/test/test-heap-classes.js
@@ -205,19 +205,49 @@ test('sloppy option', t => {
 
 const RawGreeterI = M.interface('greeter', {}, { defaultGuards: 'raw' });
 
-test('raw defaultGuards', t => {
+const testGreeter = (t, greeter, msg) => {
+  const mutable = {};
+  t.is(greeter.sayHello(mutable), 'hello', `${msg} can sayHello`);
+  t.deepEqual(mutable, { x: 3 }, `${msg} mutable is mutated`);
+  mutable.y = 4;
+  t.deepEqual(mutable, { x: 3, y: 4 }, `${msg} mutable is mutated again}`);
+};
+
+test('rawValues', t => {
   const greeter = makeExo('greeter', RawGreeterI, {
     sayHello(mutable) {
       mutable.x = 3;
       return 'hello';
     },
   });
-  const mutable = {};
-  t.is(greeter.sayHello(mutable), 'hello');
-  t.deepEqual(mutable, { x: 3 });
-  mutable.y = 4;
-  t.deepEqual(mutable, { x: 3, y: 4 });
   t.deepEqual(greeter[GET_INTERFACE_GUARD](), RawGreeterI);
+  testGreeter(t, greeter, 'raw defaultGuards');
+
+  const Greeter2I = M.interface('greeter2', {
+    sayHello: M.call(M.rawValue()).returns(M.string()),
+    tortuous: M.call(M.any(), M.rawValue(), M.any())
+      .optional(M.any(), M.rawValue())
+      .returns(M.any()),
+  });
+  const greeter2 = makeExo('greeter2', Greeter2I, {
+    sayHello(mutable) {
+      mutable.x = 3;
+      return 'hello';
+    },
+    tortuous(hardA, softB, hardC, optHardD, optSoftE = {}) {
+      t.is(Object.isFrozen(hardA), true);
+      t.is(Object.isFrozen(softB), false);
+      softB.b = 2;
+      t.is(Object.isFrozen(hardC), true);
+      t.is(Object.isFrozen(optHardD), true);
+      t.is(Object.isFrozen(optSoftE), false);
+      return {};
+    },
+  });
+  t.deepEqual(greeter2[GET_INTERFACE_GUARD](), Greeter2I);
+  testGreeter(t, greeter, 'explicit rawValue');
+  t.is(Object.isFrozen(greeter2.tortuous({}, {}, {}, {}, {})), true);
+  t.is(Object.isFrozen(greeter2.tortuous({}, {}, {})), true);
 });
 
 const GreeterI = M.interface('greeter', {