diff --git a/packages/test/lib/Ribosome/Test/Error.hs b/packages/test/lib/Ribosome/Test/Error.hs
index 11dde01..bc118b8 100644
--- a/packages/test/lib/Ribosome/Test/Error.hs
+++ b/packages/test/lib/Ribosome/Test/Error.hs
@@ -9,39 +9,46 @@ import Ribosome.Host.Data.RpcHandler (Handler)
 
 -- |Resume an effect and convert its error from @'Stop' err@ to @'Error' 'TestError'@.
 resumeTestError ::
+  HasCallStack =>
   ∀ eff err r .
   Show err =>
   Members [eff !! err, Error TestError] r =>
   InterpreterFor eff r
 resumeTestError =
-  resumeHoistError (TestError . show)
+  withFrozenCallStack do
+    resumeHoistError (TestError . show)
 
 -- |Run a 'Handler', converting the @'Stop' 'Report'@ at its head to @'Error' 'TestError'@.
 testHandler ::
+  HasCallStack =>
   Member (Error TestError) r =>
   Handler r a ->
   Sem r a
 testHandler =
-  stopToErrorWith (TestError . reportMessages)
+  withFrozenCallStack do
+    stopToErrorWith (TestError . reportMessages)
 
 -- |Run a 'Handler' in a new thread and return an action that waits for the thread to terminate when sequenced.
 -- Converts the @'Stop' 'Report'@ at its head to @'Error' 'TestError'@ when it is awaited.
 testHandlerAsync ::
+  HasCallStack =>
   Members [Error TestError, Async] r =>
   Handler r a ->
   Sem r (Sem r a)
-testHandlerAsync h = do
-  thread <- async do
-    runStop h
-  pure do
-    testHandler . stopEither =<< note (TestError "async handler didn't produce result") =<< await thread
+testHandlerAsync h =
+  withFrozenCallStack do
+    thread <- async do
+      runStop h
+    pure do
+      testHandler . stopEither =<< note (TestError "async handler didn't produce result") =<< await thread
 
 -- |Interpret @'Stop' err@ to @'Error' 'TestError'@ by using @err@'s instance of 'Reportable'.
 testError ::
-  ∀ err r a .
+  ∀ err r .
+  HasCallStack =>
   Reportable err =>
   Member (Error TestError) r =>
-  Sem (Stop err : r) a ->
-  Sem r a
-testError =
-  testHandler . mapReport . raiseUnder
+  InterpreterFor (Stop err) r
+testError ma =
+  withFrozenCallStack do
+    testHandler (mapReport (raiseUnder ma))