diff --git a/explorer/interpreter/action_stack.cpp b/explorer/interpreter/action_stack.cpp
index 7f24d7ecb181..24792210872b 100644
--- a/explorer/interpreter/action_stack.cpp
+++ b/explorer/interpreter/action_stack.cpp
@@ -131,6 +131,7 @@ auto ActionStack::FinishAction() -> ErrorOr<Success> {
     case Action::Kind::ExpressionAction:
     case Action::Kind::LValAction:
     case Action::Kind::PatternAction:
+      CARBON_FATAL() << "This kind of action must produce a result: " << *act;
     case Action::Kind::ScopeAction:
       CARBON_FATAL() << "ScopeAction at top of stack";
     case Action::Kind::StatementAction: